in the name of allah, most gracious, most merciful

IN THE NAME OF ALLAH, MOST GRACIOUS, MOST MERCIFUL

INVERTEBRATE PALEONTOLOGY

Prof. Abdelbaset Sabry El-Sorogy Professor of Paleontology and Stratigraphy Department of Geology and Geophysics, College of Science King Saud University, Riyadh, Saudi Arabia Zagazig University, Zagazig, Egypt

Dr. Mohamed Naguib Al-Sabrooty Associate Professor of Palynology Department of Geology and Geophysics, College of Science King Saud University, Riyadh, Saudi Arabia

Dr. Mohamed Youssef Ali Mohamed Associate Professor of Micropaleontology & Stratigraphy Department of Geology and Geophysics, College of Science King Saud University, Riyadh, Saudi Arabia South Valley University, Qena, Egypt

© King Saud University Press, 2015 King Fahd National Library Cataloging-in-Publication Data El-Sorogy, Abdelbaset Sabry Invertebrate paleontology. / Abdelbsaet Sabry El-Sorogy ; Mohamed Naguib Al-Sabrooty ; Youssef Ali Mohamed .- Riyadh, 2014 146 p., 21 x 28 cm ISBN: 978-603-507-339-4 1- Paleontology I-Mohamed Naguib Al-Sabrooty (co. author) II-Youseff Ali Mohamed (co. author) III-Title 560 dc

1436/844

L.D. No. 1436/844 ISBN: 978-603-507-339-4

This book has been published based on the approval of the Academic Council of the University in its 15th session of the academic year 1434/1435 H., which was convened on 24-4-1435 H. (24-2-2014), after meeting the terms of scientific refereeing.

All publishing rights are reserved. No part of the book may be republished or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or via any storage or retrieval system, without written permission from King Saud University Press.

PREFACE

The present student book is prepared based on the syllabus of the “Principals of Invertebrate Paleontology” course (Geo 243) of the Geology and Geophysics Department, College of Science, King Saud University. The specific goals of invertebrate macro-paleontology are: 1. 2. 3. 4. 5. 6.

To identify the geologic range of the different fossil groups. To include enough information about morphology, terminology and classification for each phyla. To differentiate between different phyla and classes. To identify the basis of classification of the different fossil groups. To understand the ecology and mode of the life of the different phyla. To give enough information on stratigraphy throughout the fossil record of invertebrates to allow determination of relative geologic age.

This student book includes 14 chapters. All chapters begin with the objectives and end with questions that measure knowledge, understanding and mental and practical skills throughout the chapter. Most chapters include anatomy, morphology, classification, ecology and modes of life. Many of the bivalve, gastropod, scleractinain, echinoderm and bryozoan photos (without references) were done through field trips and research along the Red Sea coast for the first author. Chapter I discusses the requirements of fossilization, modes of fossil preservation, fossil record, index fossils and importance of fossils. Chapter II is concerned with the classification and nomenclature of living organisms from the following points of view: taxonomic levels, binomial nomenclature and nomenclature problems. Chapter III deals with morphology, structural grades, classification, fossilization and ecology and mode of life of phylum Porifera. Chapter IV discuses the morphology and classification of Phylum Cnidaria as well as distribution, types and ecological parameters of coral reefs. Chapters V and VI deal with the morphology and taxonomy of Phylum annelida and class Trilobita respectively. Chapters VII, VIII and IX deal with anatomy, morphology, classification, ecology and modes of life for classes gastropoda, cephalopoda and pelecypoda respectively. Chapter X discuses Phylum Brachiopoda from the following points of view: morphology, homomorphy, taxonomy and modes of life. Chapter XI deals with the zoarial morphology and growth-forms, classification and ecology of Phylum Bryozoa. Chapter XII discuses morphology, anatomy, taxonomy and modes of life of Phylum Echinodermata, while Chapters XIII and XIV deal with morphology and taxonomy of Class Graptolithina and trace fossils respectively.

v

CONTENTS

Page Preface........................................................................................................................................................... v Chapter I: Introduction ............................................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Paleontology and Fossils .................................................................................................................... Fossilization ........................................................................................................................................ Requirements of Fossilization............................................................................................................. Modes of Fossil Preservation .............................................................................................................. Fossil Record ...................................................................................................................................... Index Fossil......................................................................................................................................... Sampling of Fossils............................................................................................................................. Importance of Fossils .......................................................................................................................... Questions on Fossils and Fossil Record..............................................................................................

1 1 1 1 1 2 2 5 6 6 6 7

Chapter II: Classification and Nomenclature............................................................................................ Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Taxonomic Levels .............................................................................................................................. Binomial Nomenclature ...................................................................................................................... Nomenclature Problems ...................................................................................................................... Questions on Classification and Nomenclature ..................................................................................

9 9 9 9 10 11 13

Chapter III: Phylum Porifera ..................................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................ Structural Grades ................................................................................................................................ Classification ...................................................................................................................................... Fossilization ........................................................................................................................................ Ecology and Mode of Life .................................................................................................................. Questions on Phylum Porifera ............................................................................................................

15 15 15 15 17 19 20 21 22

Chapter IV: Phylum Cnidaria .................................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................

25 25 25 25

vii

Contents

Classification ...................................................................................................................................... Solitary and Colonial Forms ............................................................................................................... Coral Reefs ......................................................................................................................................... Questions on Phylum Cnidaria ...........................................................................................................

27 35 37 40

Chapter V: Phylum Annelida ..................................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................ Reproduction....................................................................................................................................... Classification ...................................................................................................................................... Questions on Phylum Annelida ..........................................................................................................

43 43 43 43 44 46 47

Chapter VI: Class Trilobita ........................................................................................................................ Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................ Stratigraphical Use.............................................................................................................................. Classification ...................................................................................................................................... Questions on Class Trilobita ...............................................................................................................

49 49 49 49 50 51 52

Chapter VII: Class Gastropoda .................................................................................................................. Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Anatomy ............................................................................................................................................. Shell Morphology ............................................................................................................................... Classification ...................................................................................................................................... Mode of Life ....................................................................................................................................... Fossilization ........................................................................................................................................ Questions on Class Gastropoda ..........................................................................................................

53 53 53 53 55 57 58 59 60

Chapter VIII: Class Cephalopoda .............................................................................................................. Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................ Homeomorphy .................................................................................................................................... Septa and Sutures ................................................................................................................................ Siphuncle ............................................................................................................................................ Classification ...................................................................................................................................... Dimorphism in the Cephalopods ........................................................................................................ Ecology and Mode of Life .................................................................................................................. Questions on Class Cephalopoda ........................................................................................................

63 63 63 63 67 67 70 71 72 72 73

Chapter IX: Class Pelecypoda .................................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Anatomy .............................................................................................................................................

77 77 77 77

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Contents

Morphology ........................................................................................................................................ Shell Microstructure and Mineralogy ................................................................................................. Mode of Life ....................................................................................................................................... Classification ...................................................................................................................................... Questions on Class Pelecypoda ..........................................................................................................

77 83 83 85 88

Chapter X: Phylum Brachiopoda ............................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................ Shell Description and Orientation ....................................................................................................... Shell Composition and Structures....................................................................................................... Homeomorphy .................................................................................................................................... Classification ...................................................................................................................................... Ecology ............................................................................................................................................... Modes of Life ..................................................................................................................................... Geologic History ................................................................................................................................. Questions on Phylum Brachiopoda .....................................................................................................

91 91 91 91 93 95 95 96 96 97 98 99

Chapter XI: Phylum Bryozoa ..................................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Zooidal Morphology ........................................................................................................................... Zoarial Growth Forms ........................................................................................................................ Classification ...................................................................................................................................... Zoarial Growth Forms and Ecology ................................................................................................... Questions on Phylum Bryozoa............................................................................................................

101 101 101 101 102 107 107 110

Chapter XII: Phylum Echinodermata........................................................................................................ Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................ Anatomy ............................................................................................................................................. Skeleton .............................................................................................................................................. Classification ...................................................................................................................................... Class Echinoidea ................................................................................................................................. Classification of Echinoids ................................................................................................................. Modes of Life ..................................................................................................................................... Questions on Phylum Echinodermata .................................................................................................

113 113 113 113 113 115 116 119 120 121 122

Chapter XIII: Phylum Graptolithina ......................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Morphology ........................................................................................................................................ Classification ...................................................................................................................................... Questions on Class Graptolithina........................................................................................................

125 125 125 125 126 129

ix

Contents

Chapter XIV: Phylum Graptolithina ......................................................................................................... Objectives ........................................................................................................................................... Overview ............................................................................................................................................ Importance of Trace Fossils ................................................................................................................ Classification ...................................................................................................................................... Common Ichnogenera ......................................................................................................................... Questions on Trace Fossils .................................................................................................................

131 131 131 131 131 133 135

References ..................................................................................................................................................... 137 Appendix of Scientific Terms ...................................................................................................................... 141 Index .............................................................................................................................................................. 145

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CHAPTER I

INTRODUCTION

Objectives 1. 2. 3. 4. 5. 6.

Identify fossils and fossilization process. State the requirements of fossilization. Define mold, cast, replacement and carbonization. Discuss why fossil record is incomplete and biased. Compare between recrystallization and permineralization. List the importance of fossils. Overview

Fossils are remains or traces of living organisms. Fossilization is the transfer of the organism from the biosphere to the lithosphere. Fossil process includes mortality, taphonomic processes and diagenesis. Fossilization requires a hard skeleton and rapid burial in suitable sediments. Most skeletons are altered during fossilization, some are unaltered and few preserve with both soft tissues and hard skeleton. The fossil record is incomplete and biased. Fossils, especially index ones, have many uses in stratigraphy and other related fields. Paleontology and Fossils Paleontology is the study of life through geologic time, and therefore is based on the principals and methods of both biology and geology (Boardman et al., 1987). Fossils are the remains or traces of living organisms (Fig. I.1) that lived in the geological ages and are buried in the sediment and preserved in a natural way with little or many morphological features of the original organism. The vast majority of fossils are found in sedimentary rocks. The concentration and distribution of fossils vary markedly, both vertically and horizontally, within sedimentary units. In some cases, an entire sedimentary unit may be composed of fossils, and a good example is the Nummulitic limestone in Middle Eocene rocks along the Nile Valley, Egypt. Fossilization Fossilization is the transfer of the organism from the biosphere to the lithosphere. The life cycle of the organism passes through the following sequence: birth, growth, reproduction, aging, death, and decomposition or decay or both, and then it converts to elements that quickly enter the cycle of life as food for others.

1

2

Invertebrate Paleontology

Fig. I.1. Some types of fossils. (A) Rugasan corals (invertebrates). (B) Imprint of fish (vertebrates) on soft sediments.

Fossilization processes A journey that the organism passes through (from the moment of death to becoming a fossil) can be summarized in the following three points: 

 

Mortality: The reasons for the death of organisms are numerous. The common one is aging, which is usually not reached by the majority of organisms. There are diseases, parasites, lack of food and oxygen, disasters and climate changes and severe disruption of food chains. It is difficult to detect the causes of death in fossils. Taphonomic processes: It means the changes take place to the organism after death and burial in sediments. The most important of these processes are decomposition and breakage, as well as orientation and dispersion. Fossil diagenesis: It means the changes that take place to the skeleton after burial in sediments. Examples of these processes are: solution, dissolution, replacement, recrystallization, compaction, and encrustation. Requirements of Fossilization

The requirements of fossilization are presence of a hard skeleton (Table 1). In spite of this, there are rare cases of soft skeleton preservation, rapid burial in sediments, and burial in less porous and permeable sediments. Modes of Fossil Preservation 1. Preservation without alteration In rare cases, soft parts may be preserved (Fig. I.2) due to freezing of organisms, such as the mammoths of Siberia, mummification of remains in dry climates and entrapment of organisms in resin or amber or in oil seeps. Also, hard parts consisting of calcite, silica and calcium phosphate such molluscs, brachiopods, bryozoans, etc. may be preserved without alteration (Fig. I.3), especially those from the Quaternary and Tertiary periods.

Introduction

3

Table I.1. Materials forming the skeletons of living organisms. Inorganic

Organic

Silica (opal): Radiolaria and diatom

Cellulose: Plants

Calcium carbonate (Calcite or aragonite): Mullusca, echinodermata, bryozoa…

Chitin: Insects, some brachiopods and trilobites

Calcium Phosphate: Vertebrate bones and some brachiopoda

Spogine: Porifera

Others such as halidates, iron ores and suphates

Collagen: Some corals Protin: Graptolites

Fig. I.2. Preservation without alteration. (A) Mammoth from Siberian ice. (B) Insect entrapped in resin or amber.

Fig. I.3. Preservation without alteration. (A) Brachiopod shells. (B) Pelecypod shells.


4

2. Preservation with alteration There are many types of preserved fossils with alteration in the hard skeletons (Fig. I.4) which can be summarized in the following:    

Carbonization: Change by a chemical action of the original plant or animal material to a thin film of carbon that outlines the shape of a part or the entire organism. Permineralization: Deposition of mineral material, most commonly of calcium carbonate, silica, pyrite, and dolomite from underground solutions in pore spaces of buried remains. Recrystalization: Conversion of less stable compounds (such as the aragonite form of calcium carbonate of some clams and snails) into a more stable form (such as the calcite form of calcium carbonate). Replacement: Complete replacement of skeletal tissues (molecule by molecule) by new mineral material such as calcite, dolomite, silica compounds, and iron compounds. An example is petrified wood.

Fig. I.4.

Preservation with alteration. (A) Carbonization. (B) Permineralization. (C) Replacement. (D) Internal and external molds of a cephalopod shell.

Molds and casts Molds It is a removal by a dissolution of organic material buried in sediment; a void left in the rock is a mold (e.g. an imprint). Molds can be internal (expressing the shape of the inside of a shell or other feature) or external (expressing the shape of the outside of the object).

Introduction

5

Casts It is the filling of a mold (void) with sediment or mineral material, thus preserving the shape (internal or external) of the organic feature. Trace fossils Trace fossils are preserved structures in sedimentary rocks and express the vital activity of organisms such as movement, nutrition, permanent or temporary habitat without the presence of a body fossil or parts of it. There are many types of trace fossils, the main groups being:    

Tracks and trails: Footprints of animals and birds. Indications of movements by invertebrates (Fig. I. 5). Burrows: Excavations made by worms and other animals such as clams, crabs, shrimp, or fish as they tunnel into sediments. Borings: Drill holes bored through shells by predator snails or other organisms; holes bored into rock by rock-boring organisms such as clams, worms, and certain crustaceans. Coprolites: Fossilized animal excrement; may give evidence of diet, animal size, and habitat.

Fig. I. 5. Traces of movement (locomotion) within soft sediments on sea floor.

Fossil Record Fossil record is the number of fossils that we know through publications in the literature, magazines and scientific journals. There is no doubt that the number of fossils known in the fossil record is much less (5%) than the complete number that lived throughout geologic time. The fossil record is both incomplete and biased. Fossil record is incomplete due to the following reasons: 1. 2. 3.

As a general rule, the organism is not fossilized. If the organism is fossilized, it may be eroded or dissolved. Researchers do not discover all fossils in all sedimentary rocks.

Fossil record is biased due to the following reasons: 1.

Some organisms have skeletons and others do not. Insects are the most abundant living animal group, yet the percentage of fossil insects is only about one percent.

6 2. 3. 4. 5.


The diversity of materials from which the skeletons are formed. Calcitic skeletons for example are preserved better than aragonitic ones. Marine organisms have a better chance for preservation than non-marine ones. Mollusk shells accumulating on beaches may be broken and destroyed by wave action. The stratigraphic bias: More research has been done on Cenozoic and Cretaceous rocks than on older rocks. Index Fossils

These are fossils used in the determination of the relative time of the sediments bearing them. Index fossils are characterized by: 1. 2. 3. 4.

Short stratigraphic range (in other words, rapid evolution). They appeared and became extinct in a limited time. Wide geographical range. Easy to determine, even by a non-esecialist. High numerical abundance that allows to find them easily. Sampling of Fossils

Macrofossils can be collected directly from sedimentary rocks using a geologic hammer and chisel. These tools must be good and manufactured of solid steel which does not send out fragments when used. Also, gloves and glasses are used during fieldwork. After collecting samples, they are kept in containers suitable for their condition. They are collected in bags when fossils are solid and may be wrapped in paper, newspapers or cotton and are put in cardboard boxes when fossils are delicate. It is interesting to note that the fossils collected from the floors of the valleys and foothills of the mountains often represent the best cases of conservation because they had been separated from the rocks containing them in a natural way, as they are influenced by factors of weathering over a long time and very slowly. It is difficult sometimes to know the bearing rocks of such fossils. Importance of Fossils The following are some of the uses of fossils:        

Determination of the relative age of rocks containing them. Study of sedimentary paleoenvironments. Identification of paleoclimate. Determination of the paleoecology of rocks containing them. Study of the evolution of life on earth. Determination of the localities of oil and some economic resources. Support for the theory of plate tectonics. Study of paleogeography.

Introduction

7

Questions on Fossils and Fossil Record 1st Question: Choose the correct answer 1.

The process of carbon enrichment of organic-rich remains through their burial and heating. a) Carbonization b) Replacement c) Permineralization

2.

Deposition of mineral material, from underground solutions in pore spaces of buried remains. a) Carbonization b) Replacement c) Permineralization

3.

Conversion of less stable compounds into a more stable form, without change in chemical composition of the skeleton. a) Carbonization b) Replacement c) Recrystalization

4.

Preserved structures in sedimentary rocks express the vital activity of organisms. a) Trace fossils b) Replacement c) Moulds

5.

Study of microscopic fossils. a) Macropaleontology b) Micropaleontology

6.

Study of macroscopic fossils. a) Macropaleontology b) Micropaleontology

7.

Insects, some brachiopods and arthropods consist of: a) Chitin b) Spongin

c) Cellulose

Skeletons of some sponges and diatoms consist of: a) Chitin b) SiO2

c) Cellulose

Skeletons of bones and some brachiopods consist of: a) Ca5(OH)(PO4)3 b) SiO2

c) Cellulose

8. 9.

10. The changes take place to the organism after death and burial in sediments. a) Mortality b) Biostratonomy c) Diagenesis 11. The changes take place to the skeleton after burial in sediments. a) Mortality b) Biostratonomy c) Diagenesis 2nd Question: Give the scientific term to the following definitions 1. 2. 3.

The process of carbon enrichment of organic-rich remains through their burial and heating. Deposition of mineral material from underground solutions in pore spaces of buried remains. Conversion of less stable compounds into a more stable form, without change in the chemical composition of the skeleton. 4. The impression that the buried object made in the surrounding sediment. 5. Preserved structures in sedimentary rocks express the vital activity of organisms. 6. Remains or traces of living organisms. 7. Transportation of an organism from the biosphere to the lithosphere. 8. Preserved structures in sedimentary rocks that express the vital activity of organisms. 9. Study of life through geologic time. 10. The changes take place to the organism after death and burial in sediments. 11. The changes take place to the skeleton after burial in sediments.


8 12. 13. 14. 15.

Study of invertebrate fossils. Study of vertebrate fossils. Number of fossils that we know through publication. Type of fossils used in determination of relative time of the sediments bearing them.

3rd Question: Complete 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Examples of preservation without alterations: …………… and …………… Examples of preservation with alterations: …………… and …………… Paleontology is the study of life through geologic time by means of …………… Fossils are remains or traces of …………… …………… are scientists who study fossils. …………… is the study of microscopic fossils. …………… is the study of macroscopic fossils. …………… is the study of invertebrate fossils. …………… is the study of vertebrate fossils. Fossilization is the transfer of organism from …………… to …………… Fossilization includes the following processes: ……………, …………… and …………… Index fossils are characterized by……………, …………… and ……………

4th Question: Justify 1. 2. 3.

There is a relationship between porosity and permeability of sediments and fossilization of an organism. Fossil record is incomplete. Fossil record is biased.

5th Question: Write down on 1. 2.

Index fossil Importance of fossils

6th Question: Write the modes of reservation

CHAPTER II

CLASSIFICATION AND NOMENCLATURE

Objectives 1. 2. 3. 4. 5. 6.

Define kingdom, subspecies and species Compare between genus and species nomenclatures. State the taxonomic levels of living organisms. Discuss the binomial nomenclature of organisms. Differentiate between objective and subjective ranks. List the main nomenclature problems. Overview

Kingdom is the largest taxonomical unit and includes a large number of organisms. There are five kingdoms: Animalia, Planata, Fungia, Protista and Monera. The species is the essential unit in an organism taxonomy and is the only objective taxonomical unit. The next large unit, which includes a related group of species, is a genus. A group of genera form a family, and a group of families form an order and so on until Kingdom. Genus names must be in Latin and may take the name of localities, scientist names and definite characters. Species names must also be in Latin and may take the name of a researcher, a locality, a character, a continent or a geologic period. Taxonomic Levels Due to the high number of organisms, it is difficult for a researcher to study this number without a definite system that facilitates this study. This system classifies organisms into groups according to the relationship between them and the stages of their evolution. At first, organisms were classified into two major groups according to the nature of living organisms: kingdom Animalia and kingdom Planata. Now these have became five (or six) kingdoms; kingdom Fungia, kingdom Protista and kingdom Monera, in addition to the last mentioned two kingdoms. Some researchers spilt the Monera into two separate kingdoms. The kingdom is the largest taxonomical unit and includes a large number of organisms. The kingdom is classified into phyla, and each phylum includes a group of organisms that have special characteristics which differentiate them from other phyla. Also, each phylum includes a large number of organisms that are different in skeleton and soft tissues, so each phylum is classified into smaller groups called classes. Individuals of the same class are differentiated according to many bases, so a class is subdivided into small groups called orders. Each order is also subdivided into families, and each family is subdivided into genera, and each genus is subdivided into species.

9


10

The smallest taxonomical unit is the individual. Each group of individuals are similar in anatomical, functional and compositional points of view and are able to reproduce giving individuals and are also able to reproduce to become a species. The species is the essential unit in an organism taxonomy. The next large unit, which includes a related group of species, is a genus. A group of genera form a family, and a group of families form an order and so on until kingdom. Therefore, the taxonomy for all organisms is on the following levels: Kingdom Phylum Class Order Family Genus Species The species is the only objective taxonomical unit. All other levels (from kingdoms to genera) are subjective units (based on the opinions of researchers). There are other taxonomical levels, but they do not necessarily exist for each living organism. Examples for such taxonomical levels are subphylum, subclass, suborder, superfamily, subfamily, subgenus and subspecies. These additional levels are used when a problem is exposed due to the presence of few differences in the properties that characterize one of the taxonomical levels. Binomial Nomenclature Carl Linnaeus is the scientist who established the basis of binomial classification in 1758 in his book Systema Naturae. He used binomial nomenclature, which stated that each species is defined by two names. The first is the name of Genus to which the organism belongs. The second is the name of the species. These names are written with Latin and italic letters, or are underlined to distinguish them from the written text. The genus name begins with a capital letter and is considered a noun, while the species name begins with a small letter and is considered an adjective. Genus nomenclature A genus is defined as a group of species have morphological characteristics differentiate them from other genera. Genus names may simply be the Latin name of the organism, or may take the name of localities, a scientist names or definite characters. If the genus is named after a person, the end “ia” is added. For example, if the scientist name is Hamza, then the genus name is Hamzaia. An example of a genus name based on a special character is the genus Echinolampas, where Echino means spines. Then, Echinolampas means spiny lamp. Species nomenclature A species is a group of individuals that have morphological, anatomical and functional properties, and reproduce with each other giving offspring that are also able to reproduce and have the characteristics of the

Classification and Nomenclature

11

species they belong to. If a species is named after a male scientist, it ends with the letter “i”. For example, if the name is Hamza, then the species name becomes hamzai. If a species is named after a female scientist, it ends with “ae”. For example, if the name of the scientist is Amal, then the species name becomes amalae. If the species name takes the locality name (from which it was collected), then it ends with “ensis”. For example, if the name of the locality is mokattam, then the species name becomes mokattamensis. The species name may take the name of a geological period such as Miocene, hence the species name becomes miocenica. It may also take the name of a continent such as Africa, hence the species name becomes africanus. If the species name is based on a special character such as elongate, then the species name becomes elongata. Subspecies A group of individuals of a species, with simple morphological differences from the rest of the individuals of species. This is due to a change in environmental conditions (temperature, current energy, salinity) which may be due to migration into a new locality far from the original locality. In this case, the name consists of three words. For example, if the original species name is Echinolompus africanus, and a group migrated to the Nile Valley province with few morphological changes, then the subspecies name becomes Echinilampus africanus niloticus. The subspecies name has the same rules of the species name, where it begins with a small letter and is written with italic letters or is underlined. Two subspecies of the same species cannot be found at the same time and locality, but more than one subspecies of one species may be present in the same locality at different times, where each time has its special environmental conditions. It is interesting to note that the name of the person who identified the organism should be written following the binomial nomenclature and the year in which the identification was published. Nomenclature Problems Homonyms One name may sometimes be wrongly given to two different species of the same genus. This means that two species that are different in morphology might have the same name. This is forbidden by the rules of zoological nomenclature. For example, a scientist identified a new species of the genus Clyeaster in 1920 and gave it the name “Clypeaster scutaformis”, then in 1950 another scientist might give the same name for another species of the same genus. The problem is solved by considering the species name identified in 1920 as correct and the other name must be changed. Synonyms The same species was discovered in different countries and was given different names. This often happens when researches do not have access to the published literature. The problem is solved by using the first (old) name and the rest names are deleted. Example 1: When a scientist studies a certain species, he finds out that it carries three different names as follows: 1912 Laganum depressum Loriol 1920 Laganum scuteformis Lamarck 1938 Laganum tunidium Fourtau Answer: 1912 Laganum depressum Loriol is the correct name and the other names may be ignored.

12


Example 2: From the following data, which one is the correct name? 1880 Scutella Amonis Keer 1878 Scutella Planatas Rose 1910 Scutella Ammonia Said Answer: First, the correct genus and species names according to the rules of binomial nomenclature are: 1880 Scutella amonis Keer 1878 Scutella planatas Rose 1910 Scutella ammonia Said Then, arrange the names from old to new, and the correct name will be the oldest: 1878 Scutella planatas Rose 1880 Scutella amonis Keer 1910 Scutella ammonia Said Therefore, the correct name is 1878 Scutella planatas Rose. Example 3: In an attempt to identify a genus and a species, the scientist found out that the fossil took different genus names and had the species name in different literatures as follows (from old to new): 1910 Schizaster africanus Fourtau 1912 Hemiaster africanus Loriol 1920 Hemiaster africanus Rose Answer: Revise the morphological characteristics of the genera Schizaster and Hemiaster to figure out if the sample is close to anyone of them. In general, the most frequent name is most likely the correct name. Accordingly, the correct name of the genus is Hemiaster, then put the name of the author who identified the species first as follows: 1910 Schizaster africanus Fourtau But Fourtau identified that the species belongs to the genus Schizaster and this is an incorrect name. In this case, the name of the author is put between two brackets to indicate that the genus name is changed. Therefore, the correct name is Schizaster africanus (Fourtau), 1910.

Classification and Nomenclature

13

Questions on Classification and Nomenclature 1st Question: Choose the correct answer 1. 2. 3. 4. 5. 6.

Each genus includes a large number of: a) Families b) Orders

c) Species

Each family includes a large number of: a) Genera b) Orders

c) Phyla

Each order includes a large number of: a) Kingdoms b) Families

c) Phyla

The largest taxonomical units are: a) Families b) Kingdoms

c) Species

The essential unit in an organism taxonomy is: a) Family b) Kingdom

c) Species

The only objective taxonomical unit is: a) Family b) Kingdom

c) Species

2nd Question: Give the scientific term to the following definitions 1. 2. 3. 4. 5. 6. 7. 8. 9.

The essential unit in an organism taxonomy. The only objective taxonomical unit. A group of individuals that have morphological, anatomical and functional properties, and reproduce with each other giving offspring. The scientist who established the basis of classification. A group of species that have the same morphological characteristics. A group of individuals of a species, with simple morphological varieties from the rest of the individuals of the species. One name is given to many species of the same genus. Two species that are different in morphology have the same name. The same species is discovered in many countries and then took different names.

3rd Question: Complete 1. 2. 3. 4. 5. 6. 7.

Organisms are classified into five kingdoms: ……………, ……………, ……………, …………… and …………… If the scientist name is Hamza, then the genus name is ……………. If the male scientist name is Hamza, then the species name becomes …………… If the female scientist name is Amal, then the species name becomes …………… If the name of the locality is mokattam, then the species name becomes …………… If the species name is due to a “character” elongate, then the species name becomes …………… Among the nomenclature problems are …………… and ……………

4th Question: Justify 1.

Two subspecies of the same species cannot be found at the same time and locality.


14 5th Question: Define the following terms 1. 2. 3.

Homonames Synonames Species

6th Question: Solve the following problems 1.

When a scientist studies a certain species, he finds out that it has three different names in different time periods as follows: 1912 Laganum depressum Loriol 1920 Laganum scuteformis Lamarck 1938 Laganum tunidium Fourtau

2.

From the following data, which one is the correct name? 1880 Scutella Amonis Keer 1878 Scutella Planatus Rose 1910 Scutella Ammonia Said

3.

On trial to identify a genus and a species, the scientist found out that the sample took different genus names and had the same species name in different literatures as follows (from old to new): 1910 Schizaster africanus Fourtau 1912 Hemiaster africanus Loriol 1920 Hemiaster africanus Rose

CHAPTER III

PHYLUM PORIFERA

Objectives 1. 2. 3. 4. 5. 6.

State the geologic range of the Porifera. List the structural grades of the Porifera. Compare between Megascleres and Microscleres. Compare between Demospongia and Calcarea. Identify the morphology of Porifera. Differentiate between structural grades of Porifera. Overview

Sponges are multicellular organisms between protozoa and metazoan. They are filter-feeding with a single layer of flagellated cells, and they drive a unidirectional current of water through the body. They are aquatic, epibenthos and sedentary, and they are found in all marine and many freshwater habitats. They can be found in rivers and streams, from rock pools to the deep ocean depths, and from frozen arctic seas to the warm tropical seas. Skeletons are made of needlelike spicules, organic fibers, or calcareous laminae and are the only parts preserved in fossils. Sponges are characterized by their ability to regenerate (from Cambrian to Recent) with 10,000 species. Morphology The cellular part of the sponge body consists of a radically symmetrical to an irregularly massive or sheetlike group of cells arranged about a canal system. Sponges include a system of pores (also called Ostia) and canals (Fig. III.1), through which water passes. Water movement is driven by the beating of flagellae, which are located on specialized cells called choanocytes (collar cells). The following are the main types of cells (Fig. III.2), from which the sponge bodies are built up (http://www.earthlife.net/inverts/porifera.html):   

Choanocytes: Vase shaped cells with a collar of fine fibrils connected by microvilli. This is a filter which strains out the smallest food items from the water. Extending from the center of this collar is the single flagellum whose beating drives the water currents that keep the sponge alive and healthy. Pinacocytes: These form much of the epidermis of sponges. Generally, they cover the exterior and some interior surfaces. They can change their size (they are contractile) and can therefore change the size of the openings of the Ostia, thus controlling the flow of water through the sponge. Amoebocytes: They have several forms, and are mobile and move around within the sponge body. Archaeocytes are the basis of some asexual reproductive gemmules. If an amoebocyte secretes the spongin

15

16

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fibres of the skeleton, then it is called a spongioblast. If it secretes the spicules, then it is called a scleroblast. If it has star shaped and secrete collagenous fibrils, then it is called a collencyte. Lophocytes: They are a type of amoebocyte and they are the most motile of the sponge cells moving around relatively freely within the mesohyl where they are important in the secretion of fibrils.

Fig. III.1. Generalized morphology of a branching thin-walled sponge (http://en.wikipedia.org/wiki/Sponge).

Fig. III.2. Diagram of a microscopic section of a sponge wall showing characteristic cells and their distribution (Rigby, 1987).

Phylum Porifera

17

Reproduction Sponges reproduce both sexually and asexually (Fig. III.3). Most sexually reproducing species are hermaphrodites. The sperms are shed into the water and taken up by other sponges. Individuals with eggs use special cells called archaeocytes to transport the sperms to the eggs. Zygotes develop into ciliated larvae that are released into the water and eventually settle and develop into a sponge. The larvae may settle directly and transform into adult sponges, or they may be planktonic for a period of time. Adult sponges are generally assumed to be completely sessile, but a few studies have shown that adult sponges in a variety of species can crawl slowly (Bond and Harris, 1988). Asexual reproduction is either by budding that break off after attaining a certain size, or more commonly the production of gemmules which are the clusters of cells surrounded by a protective coat.

Fig. III.3. Life cycle of a sponge (http://en.wikipedia.org/wiki/Sponge).

Skeleton The skeletons of sponges are secreted by specialized cells, the spongocytes and sclerocytes. The skeleton is formed of either crystalline-to-microgranular calcium carbonate, silica (secreted by sclerocytes), or spongin fibers (secreted by spongocytes). The nomenclature of spicules (Figs. III.4 and III.5) depends on the number of axes (monaxon, triaxon, or tetraxon) and size (megasclere and microsclere). Structural Grades Sponges have three different grades of wall structures and the mechanism of water flow through wall (Fig. III.6). Asconoid sponges Sponges that are in the form of a simple tube are perforated by pores. It is the simplest system. Water enters through pores into a single large central cavity (the spongocoel) which is lined with choanocytes. There is a single opening to the outside called osculum.

18


Syconoid sponges Sponges tend to be larger and with thick, folded wall than asconoids, and the pores that penetrate wall are longer, forming a system of simple canals. These canals are lined by collar cells, and the flagellae move water from the outside into the spongocoel and out the osculum. Leuconoid sponges The largest and the most complex sponges. These sponges are made up of masses of tissues penetrated by numerous canals. The canals lead to numerous small chambers lined with flagellated cells. Water moves through the canals, into these chambers, and out via a central canal and osculum. Sponges in class Calcarea are considered being the most primitive group, and having asconoid, synconoid and leuconoid members. The Hexactinellida and Demospongiae groups have only leuconoid forms.

Fig. III.4. Nomenclature of common microscleres. Spicules are shown in comparison to a ray fragment of a megasclere (Rigby, 1987).

Phylum Porifera

19

Fig. III.5. Nomenclature of common Megascleres (Rigby, 1987).

Classification The classification of modern sponges depends on the anatomy of soft body and nature, form, and composition of the skeleton. Three classes are included within the Porifera. Class Demosongia It contains 95% of living sponge species, with siliceous spicules and/or spongin and sometimes with foreign inclusions, monaxons or tetraxons. Spicules rays usually diverge at 60° or 120°. All are leuconoid and all are marine except for Spongillidae (the freshwater sponges). From Cambrian to Recent, 600 living genera and 390 fossil genera.

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Fig. III.6. Structural grades of a sponge (http://en.wikipedia.org/wiki/Sponge).

Class Calcarea Poriferans with a skeleton of calcareous spicules or porous calcareous walls are lacking spicules, exclusively marine, aspiculate sponges beadlike or cystose linear, branched, or massive. The spicules are straight or have three or four rays:aAscon, sycons or leucons. From Cambrian to Recent, there are 115 fossil genera. Class Hexactinellida Poriferans with a skeleton of siliceous hexactines, with spicular rays, diverge at 90°. Nearly all are deepsea forms, most are radially symmetrical, exclusively marine, usually of leucons. From Lower Cambrian to Recent, there are 295 fossil genera. Fossilization The fossil record of Porifera is poor to a large extent. This is due to the following factors: 1. 2. 3.

It is one of the small sized phyla. The skeleton is formed of spicules and after death become loose. Also the presence of spongin (organic material formed all or part of structure), reduces the chances of fossilization.

However, the spicules may accumulate together making up vital structures, or cover large areas of the seabed, as do siliceous spicules covering some areas of the deep ocean. The rock may consist of siliceous spicules completely and it is called spiculerite and spiculeritic chert.

Phylum Porifera

21

Ecology and Mode of Life Sponges are aquatic organisms that are mostly marine. They live as benthonic sessile epifauna. Sponges are worldwide in their distribution, from the polar regions to the tropics (Bergquist, 2001). The most important environmental factors affecting the distribution and abundance of sponges are: currents (water power), depth and rate of sedimentation. The importance of the currents is double-edged, beneficial and harmful. Water currents bring food and oxygen to poriferans and remove their wastes. The effect of currents on sponges may be harmful if increased to the extent that they affect their fixation on the bottom. The depth of the water is an indirect environmental factor, as it is affected by other factors, such as temperature, pressure, available food and oxygen, and others. As a general rule, the marine calcareous sponges are increasingly common in shallow warm environment due to the ease of the formation of lime in shallow water. The siliceous sponges become more common in cool deeper water, where silica is not affected by this environment, while lime cannot be formed there. Therefore, the presence of sediment-rich in siliceous sponges is an evidence for deep marine environment. The concerning rate of sedimentation, the most appropriate environment for living sponges, is the one protected from strong currents and a with low rate of sedimentation. Most sponges live in quiet clear waters because a sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe (Krautter, 1998).


22

Questions on Phylum Porifera 1st Question: Choose the correct answer 1. 2. 3. 4. 5. 6. 7. 8. 9.

Poriferan species are: a) epifaunal sedentary

b) infaunal sedentary

c) vagile

Poriferans are: a) aquatic

b) marine

c) aquatic mostly marine

Mode of life of porifera is: a) Plankton

b) Benthonic

c) Nekton

Most skeletons in porifera are: a) exoskeletons b) endoskeletons

c) without skeletons

Hard skeletons in porifera consist of: a) silica b) Ca Co3

c) spogine

Porifera that composed of silica spicules are abundant in: a) deep water b) shallow water c) both together The outer layer of sponges. a) Pinacocytes

b) Choanocytes

c) Mesenchyme

The inner layer of sponge. a) Pinacocytes

b) Choanocytes

c) Mesenchyme

The gelatinous middle layer of sponge. a) Pinacocytes b) Choanocytes

c) Mesenchyme

10. Calcareous sponges are abundant in: a) deep water b) shallow water

c) both together

d) all are possible d) no relation

d) no relation

2nd Question: Give the scientific term to the following definitions 1. 2. 3. 4. 5. 6.

The simplest structural grade of sponge. The complex structure grade of sponge. The middle layer between the pinacocyte and choanocyte layers. Large excurrent pore through which water go out the sponge. Pores through which water enter the sponge. The intermediate structure grade of sponge.

3rd Question: Complete 1. 2. 3. 4. 5.

Calcareous sponges increase in ……………… environment. Siliceous sponges increase in ……………… environment. The three modes of sponge structures are ………………, ……………… and ……………… Sponge spicules composed of one or more of the following components: ………………, ……………… and ……………… The basis of classification of porifera are ……………… and ………………

Phylum Porifera

6. 7. 8. 9. 10. 11. 12. 13. 14.

Water enters sponges through small pores called ……………… and exits through larger ones called ……………… ……………………… is the outer layer of sponge. ……………………… is the inner layer of sponge. ……………………… is the gelatinous middle layer of sponge. The functions of pinacocytes are ……………… and ……………… The functions of choanocytes are ……………… and ……………… The function of sclerocytes and spongocytes is ……………………………… The nomenclature of sponge spicules depends on ……………… and ……………… The most environmental factors affecting the distribution and abundance of sponges are ………………, ……………… and ………………

4th Question: Justify 1. 2.

23

Most sponges live in quiet and clear waters. Fossil record of porifera is poor.

5th Question: Label

24 6th Question: Write the skeleton grade


CHAPTER IV

PHYLUM CNIDARIA

Objectives 1. 2. 3. 4. 5. 6. 7.

Identify the geologic range of Cnidaria. Compare between Anthzoa and Hydrozoa. Identify the ecology of coral reefs Explain the theory of coral reef development. Identify the morphology of Cnidaria. Differentiate between Rugosa and Scleractinia. Discuss the environmental parameters controlling reef formation. Overview

Solitary and colonial invertebrates are simple in their composition, but their cells are more specialized than sponges. Cnidarians are completely aquatic, mostly marine, benthonic sessile. Some of them stick to floating objects such as plants, others are capable to limited movement on the bottom, and very few are able to swim or float. They are radial or bilateral symmetry. They have two body forms: Polyp and Medusa. The wall consists of ectoderm, endoderm and mesoglea with a mouth surrounded by tentacles, but no separated anus. Stinging cells (nematocyst), from which the name of the phylum is derived. From Proterozoic to Recent. Morphology The cnidarian body consists of two layers: epidermis and gastrodermis separated by non-cellular mesoglea. The functions of the epidermis are neurons, muscle cells and communication. Cnidarians have no excretory, respiratory or circulatory systems. The digestive system consists of a central mouth leading to the intestinal lumen. The digestion residue returns again through the mouth. The tentacles are structures surrounding the mouth to collect food and carry stinging cells (Fig. IV.1). Life cycle In the life cycle of individuals in Cnidarians (Fig. IV.2), two generations (Fig. IV.3) may alternate, or only one of them may appear. The first phase is called the polyp form, which is somewhat cylindrical, tubular and consists of a basal disc fixed on the substratum. The body wall has a small amount of mesogloea and surrounds the gastric cavity. The mouth is directed upward and surrounded by tentacles. It reproduces asexually as in hydroids and corals, and it is adapted to a sessile habitat.

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26


The second generation is the medusa, which takes a bell-shape or umbrella-shape. The mouth is directed downward and is surrounded by small tentacles. The body wall has a large amount of mesogloea. The body composition in the medusa form is adapted to planktonic life or swimming. It reproduces sexually.

Fig. IV.1. Stinging cells (nematocyst) and the mechanism of stinging in Cnidaria (http://en.wikipedia.org/wiki/Cnidaria).

Fig. IV.2. Alternation of a generation in the life cycle of Cnidaria (http://en.wikipedia.org/wiki/Cnidaria).

Phylum Cnidaria

27

Fig. IV.3. Basic body forms in Cnidaria (http://en.wikipedia.org/wiki/Cnidaria).

Skeleton Many of the cnidarian polyps have organic or calcareous external skeletons. Some of them have organic or speculate internal ones. The organic skeletons may be of chitin or horny, which are rarely preserved as fossils. The calcareous skeletons may be of calcium carbonate (calcite or aragonite) as in corals and other cnidarians. The function of cnidarians skeletons is supporting the body. Symmetry There are many types of symmetry (Fig. IV.4) in cnidarians (Oliver and Coates, 1987):    

Radial symmetry: Which occurs when two or more planes passing through the axis of symmetry that runs from the mouth to base, produce identical halves. Tetrameral radial symmetry: Occurs when two planes of symmetry at right angles to each other pass through the axis of symmetry to divide a polyp or medusa into identical quadrants. Biradially symmetrical: They can be divided into two equal parts by either of the two planes of symmetry at right angles to each other. Radiobilaterally symmetrical: Having only one plane of symmetry. Classification

The phylum Cnidaria is divided into three living classes on the basis of the phase that prevails (polyp or medusa or both), gastric cavity (divided or empty), the nature of the skeleton (external or internal or without) and the mode of life (fixed or floating).

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Fig. IV.4. Diagrammatic transverse sections of cnidarians illustrating symmetry and arrangements of mesenteries. Numbers mark the planes of symmetry. (A) Fourfold radial symmetry. (B) Biradial symmetry. (C) Apparent sixfold radial symmetry. (D) Octamerous radiobilateral symmetry. (E) Radiobilateral symmetry (Oliver and Coates, 1987).

Phylum Cnidaria

29

Class Hydrozoa Marine and fresh water Cnidaria in which the polyp stage usually dominates in alternation of generation. Both polyps and medusa radially symmetrical (Figs. IV.5 and IV.6). From Proterozoic to Recent, there are 500 genera. Class Hyrozoa includes a wide range of polypoid and medusoid animals including the following: 1. 2. 3. 4. 5.

Hyroids: Tree-like colonies, often with flexible external skeletons. They are most common at the present time, but their fossil record is poor due to their chitineous skeletons. Milleporids: Colonies with calcareous skeletons (among the most important fossils). They have the ability to form reefs with Corals. El-Sorogy (1990) identified three types of the genus Millepora from Pleistocene coral reefs of the Red Sea coast. Trachylines: Primitive pelagic medusas with no polyp generation. Siphonophores: Oceanic hydrozoans with remarkably varied numbers of both medusoid and polypoid polymorphs clustered in one colony (Oliver and Coates, 1987). Actinulids: Minute, solitary hydrozoans that live in the pore spaces within marine sands and have neither a true polyp nor a medusa.

Class Scyphozoa Exclusively marine cnidarians, mostly in the medusa stage (Fig. IV.7). Medusa and polyp have tetrameral radial symmetry, where the cavity is divided into four folds, having an impact on the outer layer. The mesogloea is often thick, the polyps are solitary individuals, and the calcareous skeletons are absent. Scyphozoans are planktonic or swimming. From late Proterozoic to Recent, there are 90 genera. Class Anthozoa Exclusively marine cnidarians. They live in solitary or in colonies. The class includes most cnidarian fossils, and only the Polyp form is present. The mouth is central and rectangular with a pharynx extending deep into the gastric cavity. The mouth is surrounded by tentacle rings (Fig. IV.8), which can be contracted within the mouth. The gastric cavity is divided vertically by mesenteries. The mesenteries are separated by a septa if present, and the mesogloea is thick. From Edicarian to Recent, there are 2300 genera. Internal or external skeletons of chitin are collagenous, calcareous or absent. Anthozoans live in most marine environments, from tidal pools to the depths of up to 6000 meters or more. On the basis of the number and symmetry of mesenteries within the gastric cavity, and the type and composition of skeletons, anthozoans are classified into three subclasses. Subclass Seriantipatharia It has solitary and colonial cnidaria, with unpaired mesenteries and weak mesenterial muscles. It includes precious black coral and a group of burrowing sea anemones. They are rarely as fossils. From Miocene to Recent, there are about 50 genera. Subclass Octacoralla It is colonial Anthozoa with eight unpaired mesenteries and eight tentacles. The skeletons are commonly internal, spicular, horny or calcitic. The external horny or aragonitic skeletons are known, and they are bilateral and superficially radial symmetry. It includes sea pens and sea fans. From Jurassic to Recent, there are about 250 genera. Among the most important examples of octacoralla is the fossil genus Heliopora with a massive aragonite skeleton and light blue color. It is one of the basic components of the coral reefs in the Indo-Pacific. Also, the red coral Tubipora (Fig. IV.9) which forms large blocks, consisting of horny tubes in cornea-like.

30


Fig. IV.5. Generalized morphology of Hydra and its wall structure (http://en.wikipedia.org/wiki/Cnidaria).

Fig. IV.6. Life cycle of Hydrozoa (http://en.wikipedia.org/wiki/Cnidaria).

Phylum Cnidaria

Fig. IV.7. Jelly fish is an example of medusas scyphozoan (http://en.wikipedia.org/wiki/Cnidaria).

Fig. IV.8. Generalized morphology of cnidarian polyps (http://en.wikipedia.org/wiki/Cnidaria).

Fig. IV.9. Red coral Tubipora.

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Subclass Zoantharia It is solitary or colonial cnidarians. It includes the most important groups of sea anemones. Polyps have pairs of mesenteries in two, four or six places. From Late Proterozoic to Recent, there are about 6000 living species that belong to 2300 genera. Calcareous skeletons of Zoantharia are composed of calcite or aragonite, excreted by the skin layer at the base of the polyp. With growth, the polyp base forms a series of radiating folds, each of which arises from a septum, grows vertically in the same radiation system. The septa extend up with polyp growth. With continued growth the polyp builds transverse plates called tabulae, or a group of smaller plates called dissepiments. The polyp occupies the upper part of the skeleton called calices, surrounded by theca. The skeleton of coral, whether solitary individuals or colonies, is called the corallum, while the skeleton of an individual is called a corallite. The skeleton between corallites of a colony is secreted by tissues called coenosarc. The subclass Anthozoa includes three groups of sea anemones (Actiniaria, Corallimorpharia and Zoanthiniaria). These groups are important in understanding the theories of evolution of coral orders and the relations among them. The most important orders of Zoantharia are: Tabulata, Heliolitida and Rugosa, (Paleozoic), and Scleractinia (Mesozoic and Cenozoic). There are also two small orders but of great importance: Heterocorallia and Cothoniida. Order Cothoniida It is small calcitic solitary and colonial corals. Cone-like or dish shaped with a lid. The septa is weak, and the arrangement of the septa is similar to that in tetracoralla. It is rare in the Middle Cambrian (extinct order), since there is only one or two genera. Order Tabulata It is calcitic corals, exclusively colonial, with slender corallites and common holes or tubes between them (Fig. IV.10). The septa is absent or short, and is usually in the form of rows of spines or low ridges. Dissepiments are present or absent. From Ordovician to Permian (extinct order), it includes about 280 genera. The order Tabulata includes massive, plates, heads, branched, or form chains of different sizes. The colony may reach a large size of up to four meters in diameter, and contain millions of individuals. Asexual reproduction is common in most Tabulata, but the central breeding and peripheral is also recorded.

Fig. IV.10. Oblique view of chain tabulate coral Halysites (Oliver and Coates, 1987).

Phylum Cnidaria

33

Order Heliolitida They are corals of calcite. They are all colonial with slender corallities, separated by coenosteum. The septa is generally present (12 septum) in the form of spines or laminar. The plates are common. From the middle Ordovician to middle Devonian (extinct order), there are about 70 genera. Asexual reproduction was common in addition to lateral multiplication. The colonies are massive, lamellar, lenticular, hemispherical, or even branched. Order Rugosa They are corals of calcite. They are either solitary (Fig. IV.11) or colonial. The order has major and minor septa. The main septa is in four corners. The minor septa is short, and is inserted between the main septa. The tabulae is almost always present. Dissepiments are also common. Walls are composed by a lateral docking of septa and dissepiments. External walls are epithecate. From middle Ordovician to late Permian, there are about 800 genera. Individuals range size is from several millimeters to about 14 cm in diameter and may reach one meter each. Colonies may reach up to 4 meters in diameter. Internal structures can be clarified through transverse, perpendicular and longitudinal cross-sections through coralities or colonies. Definition of most Paleozoic corals took place using such sections. Septa in Rugosa are separated by fossulae and are characterized by the presence of trabiculae. Rugasans are used as index fauna for Paleozoic rocks. They were hermatypic corals in the Devonian and were extinct by the end of Paleozoic.

Fig. IV.11. Solitary rugose coral (http://en.wikipedia.org/wiki/Cnidaria).

Order Heterocorallia They are calcitic, elongate corals with four axially jointed protosepta. The secondary septa in each quarter is connected to the primary septa and intertwined composed sectors like the letter Y, but each quarter does not resemble the quarter next to it. Platelets are present. From late Devonian to Mississippian (extinct order), there are only 5 genera. Order Scleractinia They are aragonite corals of solitary and colonial (Figs. IV.12 and IV.13) with six primary septa and successive secondary ones in multiplication of the six (6, 12, 24, 48, ……). The walls are usually perforated, and the horizontal structures are varied. Coenosteum is common in colonies. From Middle Triassic to Recent, there are about 600 genera. The calicoblastic layer is part of the epidermis responsible for the secretion of the calcareous skeleton (Fig. IV.14). The equation assumed for such a process is: Ca2+ + 2HCO3 = CaCO3 + H2O + CO2

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In hermatypic corals, zooxanthellae algae symbioses with scleractinian corals. Zooxanthellae algae removes carbon dioxide, which increases the efficiency of the reaction rates, and consequently helps in the growth of the skeleton in a faster way. Experience shows that the skeleton grows 20 times more quickly during the day than during the night.

Fig. IV.12. Living coral colony with polyps expanded (http://en.wikipedia.org/wiki/Cnidaria).

Fig. IV.13. Relation of polyp to skeleton in young solitary scleractinian coral (Oliver and Coates, 1987).

Phylum Cnidaria

35

Fig. IV.14. Postulated model for precipitation of the coral skeleton (Oliver and Coates, 1987).

Solitary and Colonial Forms Skeletons of solitary individuals take many forms (Fig. IV.15) such as fungi-shaped, cone and elongate. Scleractinian colonies take the following important forms (Figs. IV.16 and IV.17):       

Phaceloid: Individuals exist in the form of parallel or semi-parallel tubes coherent with calcareous deposits, in the form of horizontal plates, such as the genus Galaxea. Dendroid: Individuals lined up and held together to form branching forms, such as the genus Acropora. Cerioid: Form in which the wall between each two adjacent hexa-corallities becomes one wall, such as in the genus Favites. Meandroid: Individuals fit together with each other and the wall between them disappear, and consists what looks like brain-shape valleys, such as in the genus Leptoria. Placoid: Individuals are separated from each other, and each corallite has its own wall, and engage with each other by thin desipments between walls, such as in the genus Favia. Thamnasteroid: Corals lack a specific walls, and septa are converging such as in the genus Thamnasterea. Hydnopheroid: Corals with centers arranged around hills such as the genus Hydnophora.

Fig. IV.15. Solitary forms. (A) Fungi-shaped. (B) Elongate form.

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Fig. IV.16. Colonial forms. (A) Phaceloid. (B) Dendroid. (C) Cerioid. (D) Meandroid. (E) Placoid. (F) Thamnasteroid.

Phylum Cnidaria

37

Fig. IV.17. Hydnopheroid colonial form.

Coral Reefs Coral reefs are calcium carbonate buildups, secreted by corals, algae, mollusks, hydrozoans, echinoderm, etc. The following are the factors controlling the coral reef formation. Depth Depth is an indirect ecological parameter with its relationship with light, temperature, pressure, oxygen content, etc. Hermatypic corals grow in continental shelves up to 90 meters depth. Most of them grow in depths less than 50 meters. The acme grows at depths less than 20 meters. Ahermatypic corals live in depths from depths of hermatypic corals to 6000 meters. Most of them occur between the shore and 500 meters depth. Temperature Few hermatypic corals live in seas with a temperature less than 18ºC. They flourish between 25ºC and 29ºC. The uppermost temperature is 36ºC. Ahermatypic corals live in the temperatures range from temperatures of hermatypic reefs to less than 0ºC. Most of them occur between 4.5ºC and 10ºC. Salinity The salinity tolerated by scleractinians lies between 27 and 40 parts per thousands (ppt). They live best in salinities at or near the ocean normal of 36 ppt. Light The relationship between hermatypic coral and light is attributed to the presence of zooxanthellate algae within coral tissues. Ahermatypic corals do not contain algae and are independent of light. Water movement The circulation of water is necessary to supply corals with nutrients and oxygen, and to remove sediments. Corals rarely survive or live in areas where sedimentation is rapid.

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Substratum Coral planulae can settle only on a firm substratum such as bed rock, other corals, shells and skeletal parts of other sedentary organisms. In general, fine sands, silt or mud bottoms do not promote coral development. Sea level fluctuations The melting of ice at the poles affect coral reefs geometry as follows:     

When sea transgresses slowly, then the reefs grow towards land in a back-reef. When the sea transgresses quickly, then the last formed reefs will die due to the increased water depth. When the sea regressing slowly, then the reefs grow towards the sea in reef-slope. When the sea regresses quickly, then the last formed reefs will die due to exposure in air. When the sea level is stable, then the reefs will grow towards the sea through reef-talus.

Types of coral reefs According to the general shape and relationship with neighboring continents, coral reefs could be classified into three types. 1. Fringing reef It forms along the coast, and connects with continents or volcanic islands such as the Red Sea and the Gulf of Aqaba (Ras Mohammed) coral reefs. 2. Barrier reefs The coral reefs are separated from the continent by a lagoon such as the Great Barrier Reef in Australia. 3. Atolls Circular or horse-shoe coral reefs, situated on submerged islands, are usually oriented according to the prevailing wind and may include a shallow lagoon within as some Red Sea Atolls. Distribution of coral reefs Within a tropical area, two large provinces of coral reefs can be distinguished (Fig. IV.18). 1. Caribbean province Coral reefs in the Caribbean province are composed of 62 species related to 34 genera. They are characterized by an abundance of fringing coral reefs as in West India, Bahamas, and Florida. Also, they may be sometimes present along the South American coast in Venezuela and Columbia. 2. Indo-Pacific province Coral reefs in the Indo-Pacific province are composed of 700 species related to 92 genera and subgenera. This includes the Red Sea, Gulf of Aden, Arabian Gulf, Gulf of Oman, and the Indian Ocean to 26 degrees south of the equator, Australia, South China Sea, Pacific Ocean and the lower part of the Gulf of California. Corals in this province are large in number and diversity than in the Caribbean province. Also, the rate of growth in certain localities is several times higher than in the Caribbean province.

Phylum Cnidaria

Fig. IV.18. Worldwide distribution of recent coral reefs (http://en.wikipedia.org/wiki/Cnidaria).

39


40

Questions on Phylum Cnidaria 1st Question: Choose the correct answer 1. 2.

Cnidarian species are: a) all colonial

b) mostly colonial

c) all solitary

Cnidarians are: a) aquatic

b) marine


3.

Corals with calcitic skeletons have the age: a) Paleozoic b) Post-Paleozoic

4.

Symmetry in Tabulate corals is: a) bilateral b) radial

c) non-symmetrical

Symmetry in Rugose corals is a) bilateral b) radial

c) non-symmetrical

Tabulate coral skeletons consist of: a) calcite b) aragonite

c) opal

Rugose coral skeletons consist of: a) calcite b) aragonite

c) opal

Scleractinian coral skeletons consist of: a) calcite b) aragonite

c) opal

Mode of life of Anthozoans is: a) Plankton b) Sessile

c) Vagile

10. Mode of life of Scyphozoans is: a) Plankton b) Sessile

c) Vagile

11. Mode of life of Hydrozoans is: a) Plankton b) Sessile

c) Vagile

5. 6. 7. 8. 9.

12. Anthozoans were and are: a) all marine

b) aquatic mostly marine c) Terrestrial

13. Hydrozoans were and are: a) all marine


14. Scyphozoans were and are: a) all marine


15. Hydra is related to class: a) Anthozoa

b) Scayphozoa

c) Hydrozoa

16. Jellyfish is related to class: a) Anthozoa

b) Scayphozoa

c) Hydrozoa

17. Scleractinia is related to class: a) Anthozoa b) Scayphozoa

c) Hydrozoa

Phylum Cnidaria

41

2nd Question: Give the scientific term to the following definitions 1. 2. 3. 4.

An organ occupies the bulk of the mantle cavity, used for gathering food, respiration and filtration. A long bar-like loop (tie shoe) organ that supports the lophophore. A triangular area locates between pedicle foramen and the umbo of the brachial valve. Many brachiopods are similar in external features and differ in their internal ones.


The stratigraphic range of Cnidarians is …………… The stratigraphic range of Tabulate Corals is …………… The stratigraphic range of Rugose corals is …………… The stratigraphic range of Scleractians is …………… Cnidarians body consists of two layers: …………… and …………… separated by non-cellular …………… From the types of symmetry in cnidarians: …………… and …………… In the life cycle of cnidarians, two generations may alternate or only one of them appears: …………… and …………… 8. Cnidarians have an ectoderm stinging cells called …………… 9. From the factors controlling coral reef formation: …………… and …………… 10. Coral reefs classify into three types: ……………, …………… and …………… 4th Question: Justify 1. 2. 3. 4.

Paleozoic corals were better preserved than Post-Paleozoic ones? Corals are good paleoenvironmental indicators? Post-Paleozoic corals grew faster than Paleozoic ones? The most important cnidarian fossils are the corals?

5th Question: Compare between the following 1. 2. 3. 4.

Tabulata and Rugosa Scleractinia and Rugosa Anthozoa and Hydrozoa Polyp and medusa

6th Question: Label

CHAPTER V

PHYLUM ANNELIDA

Objectives 1. 2. 3. 4. 5. 6.

State examples of Recent Annelida. List the functions of cilia in Annelida. Mention the biostratigraphic importance of Annelida. List the body parts of Annelida. State the basis of classification of Annelida. Differentiate among the three main classes of Annelida. Overview

Worms have elongate bodies, a bilateral symmetry, and a high grade of segmentation (from which the phylum name was derived). They live in deep marine waters to high mountainous regions, and from the equator to polar regions. Earthworms are common examples. The castings of annelida are among the best fertilizers, as they are rich in nitrate, phosphate and potassium. Due to the absence of hard skeletons in annelida, most bodies are not preserved as fossils except some of their jaws. The common annelid fossils are their traces in the form of trails, castings, tubes, and burrows. From the Proterozoic to Recent, there are over 17,000 modern species including ragworms, earthworms and leeches. Morphology The annelids (also called "ringed worms") are formally called Annelida, from the Latin word anellus = little ring (Dictionary.com, 2009). The size of an annelid individual ranges from one millimeter as in marine representatives that live in pore spaces of floor sands to 400 centimeters as some earthworms in Australia. The density of annelida in some sandy shores of intertidal area is 32000/m2, while in terrestrial regions is 50-500/m2 according to the type of soil. External features The body is bilaterally symmetrical, and is divided into a cephalon, a trunk and a pygidium. The cephalon is small and segmented and includes mouth and sensory endings. It is divided into two parts in several marine worms. The trunk is long and segmented. The pygidium is very small and post segmented (Figs. V.1 and V.2), with an anus opening present on the ventral side. The last mentioned division is very clear in sessile annelids and less clear in vagile ones. The external cover consists of a thin non-chitinous cuticle secreted by the epidermis. Also, there are setae moved by muscles that help in movement, swimming, and fixation in burrows and tubes. The number and distribution of setae are important in the classification at higher levels of annelida. The shapes of setae are variable and useful at a lower level of classification. 43

44


A pre-segmented prostomium in front of the mouth may carry unjointed sensory antennae, stout feeding palps, sensory tentacles and sensory cirri. The parapodia are unjointed fleshy locomotary appendages on the lateral body wall of many marine annelids (Fig. V.2).

Fig. V.1. Modern representatives of annelids (http://en.wikipedia.org/wiki/Annelid).

Internal features The body consists of a flexible wall that covers the gastric cavity filled with fluids. The wall includes an external layer of ring muscles and on other layer of longitudinal muscles. Gastric fluids support the worm body and act as a hydrostatic skeleton. The gastric cavity contains several transverse septa to limit the transformation of fluid body leading to a local change in worm shape. Gastric cavity (coelom) also contains the following features (Fig. V.2): Central nervous system, closed circulatory system, digestive system, and excretory system with two simple or complicated nephridia in most segments. The digestive system consists of a mouth, pharynx, esophagus, gut, and intestine. In some marine annelids, the parapodia emit from the wall sides and are moved by complicated muscular chains. Reproduction Many species can reproduce asexually and use similar mechanisms to regenerate after severe injuries (Ruppert et al., 2004). Sexual reproduction is the normal method in species whose reproduction has been studied. The minority of living polychaetes whose reproduction and lifecycles are known produce trochophore larvae, which live as plankton and then sink and metamorphose into miniature adults. Oligochaetes are full hermaphrodites and produce a ring-like cocoon round their bodies, in which the eggs and hatchlings are nourished until they are ready to emerge.

Phylum Annelida

45

Fig. V.2. Morphology of representative modern annelids. (A) Amphitrite, a tube-dwelling marine polychaete. (B) Internal organs in the anterior part of Neanthes, a crawling and swimming marine polychaete. (C) Hirudinaria, a freshwater leech with an egg capsule. (D) Ventral view of Lumbricus, the common earthworm (Robison, 1987).

Importance Earthworms support terrestrial food chains, both as prey and by aerating and enriching soil. The burrowing of marine polychaetes, which may constitute up to a third of all species in near-shore environments, encourages the development of ecosystems by enabling water and oxygen to penetrate the sea floor. In addition to improving soil fertility, annelids serve humans as food and as bait. Scientists observe annelids to monitor the quality of marine and fresh water. Although blood-letting is no longer in favor with doctors, some leech species are regarded as endangered species because they have been over-harvested for this purpose in the last few centuries. Ragworms' jaws are now being studied by engineers as they offer an exceptional combination of lightness and strength (http://en.wikipedia.org/wiki/Annelid).

46


Classification The Phylum Annelida is classified into three main classes. The bases of the classification are the composition of reproductive organs, number and distribution and shape of setae, the presence or absence of parapodia, the composition of cephalon and its appendages and nephridia (Boardman et al., 1987). Class Polychaeta Sexes usually separate high morphological variety due to modes of life, reproductive glands in several segments, simple egg and sperm tubes, parapodia common and carry several setae in definite bundles (anchor– like). Cephalon appendages are common in sessile forms. From Cambrian to Recent, there are 150 genera that include about 12,000 species (Rouse, 2002). The Class Polychaeta lives in marine environments and rarely inhabit fresh water. Several of them feed on clay or live as filter-feeders, some are predators or scavengers, and a few are parasites. Some orders of the class Polychaeta have pharyngeal jaws of solid organic matter that are able to preserve as fossils, called scolecodonts. The ideal jaw system consists of a pair of mandibles, a pair of maxillae and a pair of carriers. Recent and fossilized tubes of some genera are mostly found on hard substratum such as shell surfaces and sea weeds. They form accumulations like reefs in rocky shore areas. Class Oligochaeta Hermaphrodite earthworms, with reproductive glands in the anterior segments, cephalon undefined, parapodia absent, setae arranged on body segments, rarely in bundles, sometimes absent. Most are burrowers that feed on wholly or partly decomposed organic materials (Rouse, 1998). Some inhabit fresh water, few live in marine water, and a few are recorded as fossils from the Ordovician. Class Hirudinea Hermaphrodite worms are with anterior and posterior suckers for fixation and movement (Ruppert et al., 2004). They are characterized by the absence of parapodia and coelomic septa, a much reduced coelom, and setae are usually present. Most Hirudinea live in fresh water, less live in marine water, some live in wet lands, not recorded in fossil record, except two Jurassic genera from Germany.

Phylum Annelida

47

Questions on Phylum Annelida 1st Question: Choose the correct answer 1.

Symmetry in annelid is: a) bilateral

b) pentameral

c) tetrameral

2.

A segmented part of an annelid body and includes mouth and sensory endings: a) cephalon b) trunk c) pygidium

3.

Class Polychaeta: a) all marine c) all terresterial

4. 5.

b) most live in marine environments and rare inhabit fresh water

Sex in Class Polychaeta is: a) usually separate

b) hermaphrodite

Sex in Class Oligochaeta is: a) usually separate

b) hermaphrodite

2nd Question: Complete 1. 2. 3. 4. 5. 6.

The common annelid fossils are their traces in the form of …………… Modern annelid species include …………………………………………………… An annelid body is divided into ……………, …………… and …………… The functions of setae in annelids are …………………………………………………… The functions of gastric fluids in annelid are …………………………………………………… A gastric cavity contains several …………… to limit the transformation of fluid body leading to …………… in worm shape.


The castings of annelida are from the best fertilizers. Most bodies of annelida do not preserved as fossils.

4th Question: Write down on the following 1. 2.

Importance of Annelida. Bases of classification of Annelida.

48 5th Question: Label


CHAPTER VI

CLASS TRILOBITA

Objectives 1. 2. 3. 4. 5. 6.

Identify the geologic range of Trilobites. Differentiate between different Trilobita orders. State the basis of classification of Trilobita. Explain the trace fossils of Trilobita. Mention the mode of life of Trilobita. List the functions of limbs in Trilobita. Overview

The phylum Arthropoda is the largest invertebrate phylum (1-2 million species). Arthropods live in all known environments, from shallow to deep seas, and on terrestrial, from equator to polar regions (water and land), and many stay sometimes in air such as insects. The phylum includes insects, spiders, and scorpions, in addition to trilobites. All of these are with a segmented body that consists of cephalon, thorax and pygidium (Fig. VI.1), and pairs of limbs, with external skeletons mostly of chitin and bilateral symmetry. Ostracods and trilobites are the most important groups of arthropods in respect to biostratigraphy. The trilobites are entirely marine and vagile benthos. The skeleton is divided into three longitudinal lobs (two lateral and one axial). The body is segmented into three transverse divisions (cephalon, thorax and pygidium). They are highly diverse and of stratigraphic importance in the Cambrian and Ordovician. From Early Cambrian to Late Permian (350 my), there are 1500 genera and several thousands of species have been described. Morphology Trilobites have an exoskeleton (carapace) that covers the dorsal part of the body, and consists of chitin saturated by calcite and calcium phosphate. Thin sections indicate that the skeleton is composed of three layers: a thin dark external layer, a thick intermediate layer and a thin transparent internal layer. The external surface is mostly smooth, and sometimes carries fine or coarse granules. On the periphery, granules become very coarse or tubercles. The sizes of mature trilobite rage from 6 mm in the genus Agnostus to 75 cm in the genera Terataspis and Paradoxides. The growth of the skeleton by molting leads to the presence of several skeletons that are variable in size and shape of the same species during its life. Therefore, the identification of individuals is difficult. The morphological features of the cephalon are important in the trilobite classification. The cephalon carapace consists of a more convex middle part called a glabella and two lateral parts called cheeks that are separated longitudinally by an axial furrow (Fortey, 1990). Two eyes and facial sutures are present on the cheeks.

49

50


Fig. VI.1. Longitudinal and transverse divisions of a trilobite (http://en.wikipedia.org/wiki/Trilobite).

The three longitudinal lobs are prominent in the thorax region. The thorax is a series of articulated segments that lie between the cephalon and pygidium. The number of segments varies between 2 and 61 with most species in the 2 to 16 range (Whittington, 1997). They reach 11 segments in the genus Acaste. The pygidium may consist of one segment as in the group Olenellids from the early Cambrian, while it may reach 30 segments in the latest genera. Except the order Angostida, the Cambrian Trilobites were micropygous, while the pygidium of genera exposed after the Cambrian was smaller than the cephalon (hetropygous) or equal in size (isopygous). Very few have a pygidium longer than the cephalon (macropygous). The functions of limbs or appendages in trilobite are locomotion, feeding, respiration and sensory. Appendages Trilobites had a single pair of preoral antennae and otherwise undifferentiated biramous limbs (2, 3 or 4 cephalic pairs, followed by a variable number of thorax + pygidium pairs). Each exopodite (walking leg) had 6 or 7 segments (Hughes, 2003) that are homologous to other early arthropods. Expodites are attached to the coxa, which also bore a feather-like epipodite or gill branch, which was used for respiration and, in some species, swimming. The base of the coxa, the gnathobase, sometimes has heavy, spiny adaptations that were used to tear at the tissues of prey (Ramskold and Edgecombe, 1996). The last exopodite segment usually had claws or spines. Many examples of hairs on the legs suggest adaptations for feeding (as for the gnathobases) or sensory organs to help with walking. Stratigraphical Use Trilobites are useful in the study of the stratigraphy of Cambrian and Ordovician. Cambrian and shallow marine Ordovician rocks were subdivided into biozones depending on trilobite fossils as they are index fossils that are characterized by a limited time range and broad geographical distribution.

Class Trilobita

51

Cruziana is a trace fossil consisting of elongate, bilobed, approximately bilaterally symmetrical burrows that are usually preserved along bedding planes, with a sculpture of repeated striations that are mostly oblique to the long dimension. In Saudi Arabia, the Cambrian Cruziana member of the Sag Formation is famous for its trilobite traces. Classification The classification of trilobites is based upon the whole complex of axial and other characters such as sutures, furrows, eyes, doublure, hypostome and spinosity. They are classified into the following orders: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Order: Agnostida Order: Redlichiida Order: Corynexochida Order: Odentopleurida Order: Lichida Order: Phacopida Order: Asaphida Order: Proetida Order: Harpetida Order: Ptychopariida


52

Questions on Class Trilobita 1st Question: Choose the correct answer 1. 2.

Trilobita are a) all marine

b) all aquatic mostly marine

c) few terrestrial

Trilobita are a) benthonic sessile

b) benthonic vagile

c) benthonic sessile & vagile

2nd Question: Complete 1. 2. 3. 4. 5. 6.

The skeleton of Trilobita is divided into three longitudinal lobs: two …………… and one …………… The Trilobita body is segmented into three transverse divisions: ……………, …………… and …………… The Stratigraphic range of Trilobita is from …………… to …………… Cephalon carapace consists of a more convex middle part called …………… and two lateral parts called …………… The thorax is a series of articulated segments that lie between the …………… and …………… The functions of limbs or appendages in trilobite are ……………, ……………, …………… and ……………

3rd Question: Justify 1.

The identification of the individuals of Trilobita is difficult.

4th Question: Write down about the Stratigraphic uses of Trilobita 5th Question: Label

CHAPTER VII

CLASS GASTROPODA

Objectives 1. 2. 3. 4. 5.

Define suture line, body whorl and apical angle. State the basis of gastropod classification. List the different modes of the life of gastropods. Describe the morphology of the gastropod shell. Interpret the absence of original shells in most gastropod fossils. Overview

Gastropods are mostly marine, a few live in fresh water, and more of them are rarely terrestrial mollusks, with a flattened ventral foot for creeping and an anterior true head with eyes and other sense organs. Internal organs are twisted by “180º” torsion so that the mantle cavity faces anteriorly. Most of them are with an aragonitic shell, often helicospiral, and less often planispiral or non-coiled. They include over 80% of molluscan species. From the Cambrian to Recent, there are 611 families of gastropods, of which 202 families are extinct (Bouchet and Rocroi, 2005). Anatomy Snails are distinguished by an anatomical process known as torsion (Fig. VII.1), where the visceral mass of the animal rotates 180° to one side during development, such that the anus is situated more or less above the head. The torsion is present in all gastropods, but the opisthobranch gastropods are secondarily de-torted to various degrees (Brusca and Brusca, 2003). The torsion leads to the loss of right-paired appendages (e.g. ctenidia, gonads, nephridia, etc.). Furthermore, the anus becomes redirected to the same space as the head. However, this "rotation hypothesis" is being challenged by the "asymmetry hypothesis" in which the gastropod mantle cavity originated from one side can only be of a bilateral set of mantle cavities (Louise, 2006). Gastropods typically have a well-defined head with two or four sensory tentacles with eyes, and a ventral foot (Fig. VII.2), which gives them their name (Greek gaster, stomach, and poda, feet). The foremost division of the foot is called the propodium. Its function is to push away sediment as the snail crawls. The larval shell of a gastropod is called a protoconch. Life begins as a trochophore larvae which then develops into a veliger larvae (Fig. VII.3). The veliger is where most of the organ systems develop. Reproduction is variable, but most gastropods have separate sexes. The fertilization of the egg occurs in water. Some gastropods are hermaphrodites (having both sexes in the same individual) and some are protandric hermaphrodites, i.e., they are male first and become female as they age.

53

54


Fig. VII.1. Torsion in gastropod. (A) Early development and symmetry organs. (B) Torsion and asymmetry organs (http://en.wikipedia.org/wiki/Gastropoda).

Fig. VII.2. General morphology of a coiled gastropod (http://en.wikipedia.org/wiki/Gastropoda).

Class Gastropoda

55

Fig. VII.3. Gastropod larvae. (A) Trochophore. (B) Veliger (http://en.wikipedia.org/wiki/Gastropoda).

Shell Morphology Most shelled gastropods have a one-piece shell, typically coiled or spiraled. This coiled shell usually opens on the right-hand side. Numerous species have an operculum, which in many species acts as a trapdoor to close the shell. This is usually made of a horn-like material, but in some molluscs it is calcareous. In the land slugs, the shell is reduced or absent, and the body is streamlined. The basic shape of the gastropod shell is a long, mostly not subdivided cone. It consists of two parts: the shell spire and body whorl (Fig. VII.4). Most gastropods are of dextral coiling (Figs. VII.5 and VII.6). They rarely have sinistral coiling as genus Lanistis. Figure VII.7 illustrates the most common forms of gastropod shells.

Fig. VII.4. The gastropod shell: basic terminology (Peel, 1987).

56


Fig. VII.5. Dextral and sinistral coiling (http://en.wikipedia.org/wiki/Gastropoda).

Fig. VII.6. Gastropod shell, traditional measurements on a dextral shell in slandered orientation (Peel, 1987).

Class Gastropoda

57

Fig. VII.7. Gastropod forms. (A) Non-coiled cap-shaped. (B) Planispiral. (C) Ear-shaped. (D) Turreted-form. (E) Fusi-form. (F) Opconical. (G) Biconical, (H) Convolute. (K) Trochspiral.

Classification The classification and definition of gastropods are very difficult because they depend on soft parts such as the morphology of the osphoradia as well as the heart and nervous system, kidneys and reproductive system. These soft organs do not fossilize after death. In addition, the shell itself is made of aragonite (unstable mineral) which may dissolve in the first stages of fossilization. In the Encyclopedia of fossils (pictured Treatise), gastropods are divided into three subclasses: 1. 2. 3.

Subclass Prosobranchi. Subclass Opisthobranchia. Subclass Pulmonata.

58


Subclass Prosobranchia Most are marine inhabitants, or in other words, they live only in salt water. However, many of the members can also live in freshwater or even on land (terrestrial). Every member of this big subclass has a coiled shell. Their soft bodies have a head complete with two eyes located on the tops of two tentacles. They have a big flat foot, which they use for locomotion and on the back end of this foot is a structure called an operculum, which acts as a trap door. From Cambrian to Recent, it includes the following orders: Paleogastropoda (Bellerophone, Eumphalus, Pleurophone, Patella, Platyceras, Trochus, Maclurites), Mesogastropoda (Cerithium, Natica, Cypraea, Strombus, Nerinea), and Neogastropoda (Conus, Voluta, Buccinum, Murex). Subclass Opisthobranchia All are marine inhabitants. Most are very small, have a fragile shell and are often contained right inside their soft bodies, or they may not have a shell at all. Many of these molluscs have very colorful bodies such as sea hares, sea butterflies or pteropods (Thecostoma), sea slugs (saccoglossans and nudibranchs), canoe (Scaphandridae), and bubble shells (several families). This subclass is present from Cambrian to Recent period. Subclass Pulmonata Most of these molluscs live on land or in freshwater lakes and streams. However, a few are marine dwellers. They all breathe by means of pulmonary sacs not gills. Some have coiled shells, but many do not have a shell at all. This subclass is present from Mesozoic to Recent period. Mode of Life Active Most gastropods move freely by foot (Fig. VII.8) and others move by the foot cilia such as the freshwater species Lymmaea and Planorbis. The speed of movement varies from 7 cm/min as in the desert snail Helix, to 12 cm/min as in genus Lymmaea, to 13 cm/min as in the genus Buccinum. The genus Bullia moves on the sandy beaches at 80 cm/min.

Fig. VII.8. Active gastropod using foot to move.

Fixed Some gastropods live on rigid rocky beaches (Fig. VII.9) with cap-shape such as the genus Patella which fixes itself by suction and moves slowly at night only to algae that formed during the day. There are other examples of sessile gastropods, including some species of Cerpidula and Turritella that live on sandy bottoms with the shell top embedded in the sand. The entire sessile gastropod examples are Cerpidula, Hipponix and Rothpletzia, as well as Vermitids such as Magilus.

Class Gastropoda

59

Fig. VII.9. Fixed gastropod Patella on rocky beaches.

Planktonic The sea butterflies also known as Pteropods live in the plankton due to the presence of fins in addition to the lightness of their shells. Some of them fill the mantle cavity with air to help them to float like Lymmaea. Fossilization In spite of the large number of gastropod fossils, it is difficult to find original shells, especially from older ages. The following are the causes of poor preservation of gastropods: 1. 2. 3.

Gastropod shells are formed of aragonite, which is an unstable calcium carbonate mineral and may dissolve leaving only the molds. Most of the gastropods live in coastal littoral, which die by highly agitated currents. After death, the shell becomes empty due to the decomposition of the animal and is subject to being crushed and broken-up under the effect of waves. The morphology of gastropod shell is an important factor in bad preservation because it is hollow and is not divided internally, so it breaks easily. Sometimes, their shells may have a tapered helix that also facilitates breakage.


60

Questions on Class Gastropoda 1st Question: Choose the correct answer 1. 2. 3.

4.

5.

Gastropods are: a) all marine

b) aquatic mostly marine

The basic shell shape in Gastropoda is: a) bivalve b) hollow conical Gastropods are: a) benthonic sessile d) benthonic and plankton

b) benthonic vagile

c) mostly aquatic, few terrestrial c) septate conical c) benthonic sessile and vagile

The stratigraphic range of Gastropoda extends from: a) Ordovician to Recent b) Cambrian to Recent d) Cambrian to Cretaceous

c) Ordovician to Eocene

Gastropods are: a) filter feeders d) all options

c) Carnivores

b) Herbivores

6.

Suture line in Gastropods is: a) the intersection of septa with the inner surface of the shell b) the line separating two successive whorls

7.

Gastropod shells are: a) coiled

b) non-coiled

c) both

Most Gastropod shells are: a) coiled planispiral

b) coiled trochospiral

c) non-coiled

b) chitin

c) aragonite

b) aragonitic

c) both

8. 9.

Gastropod shells consist of: a) calcite d) all

10. Gastropod shells are: a) calcitic

11. Gastropods with long spire are: a) faster than those of short spires c) no relation

b) slower than those with short spires

12. Most gastropod fossils are preserved as: a) casts b) internal molds

c) original shells

13. Umbilicus presents in Gastropods which are: a) non-coiled c) trochospiral with tight coiling

b) planispirally coiled d) trochospiral with loose coiling

14. Symmetry in Gastropods is: a) bilateral

c) mostly non-symmetrical

b) radial

Class Gastropoda

15. Mode of life of Gastropods is: a) Plankton b) Benthonic epifaunal d) Nekton e) Sessile

61

c) Benthonic infaunal f) Vagile

2nd Question: Give the scientific term for the following definitions 1. 2.

Rotation of visceral hump, bringing mantle cavity of gastropod anterior. A type of gastropod larvae, through most of the organ systems develop and torsion begins.

3rd Question: Justify 1. 2. 3. 4. 5.

It is difficult to classify fossil gastropods. Most gastropod fossils are preserved as internal moulds. The bad state of preservation in many gastropod fossils. The definition of morphologically similar species needs a series of successive serial sectioning. Researchers think that brachiopoda is one of the extinct phylum.

4th Question: Label

CHAPTER VIII

CLASS CEPHALOPODA

Objectives 1. 2. 3. 4. 5. 6.

State the modern examples of Cephalopoda. Identify the geologic range of Cephalopoda. Compare between Cephalopoda and Gastropoda. Identify the basis of the classification of Cephalopoda. Explain the types and stratigraphic importance of suture lines. Discuss the mode of life of Cephalopoda. Overview

Cephalopoda are exclusively marine molluscs. They are the largest in terms of size, and they are the fastest of all the molluscs. They are offensive predators and have a highly specialized nervous system. They have the body of a bilateral symmetry. The advantage of cephalopoda is the ability to float and the presence of an ink sac. The importance of cephalopoda as fossil groups lies in the field of biotstratigraphy, where many of them are index fossils, particularly in Paleozoic and Mesozoic rocks. There are 800 extant cephalopod species and 11,000 extinct ones (Wilbur, 1985). Cephalopoda can be subdivided into three informal modern groups (Pojeta, 1987): 1. 2. 3.

Cephalopods with an external shell and a thin mantle as genus the Nautilus (Fig. VIII.1). They have up to 94 tentacles and are represented by five living species only. Cephalopods with an internal shell, a thick external mantle and 10 tentacles. They are represented by about 450 living species. Examples include Sepea and Spirula (Fig. VIII.1). Cephalopods with an internal shell or without a shell and a thick external mantle. They have eight tentacles and are represented by 150 species, including the octopus (Fig. VIII.1) and paper nautilus. Morphology

Shell composition and structure Most cephalopod fossils have external shells in contrast to most modern ones, which have internal shells. The basic form of the cephalopod shell is conical, subdivided internally by septa (septate conical), unlike gastropods (empty hollow). The shell of the genus Nautilus serves as an example for modern cephalopoda (Fig. VIII.2) that consists of aragonite in a matrix of conchelin. It consists of two main layers: the outer porcelaneous layer and interior nacreous layer. Septa also have the same composition as the shell.

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Fig. VIII.1. Morphology of modern representatives (http://en.wikipedia.org/wiki/Cephalopod).

of

cephalopods.

(A)

Nautilus.

(B)

Sepea.

(C)

Fig. VIII.2. Morphology of soft and hard parts of the genus Nautilus (http://en.wikipedia.org/wiki/Cephalopod).

Octopus

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The cephalopod shell is divided into two parts (Fig. VIII.3): a phragmocone which starts from the top with the initial chamber (protoconch), and the body chamber which is undivided and situated in the wider side of the shell. With successive growth the animal moves anterior, building a new septum behind. The siphuncle connects all champers. The basic cone of the cephalopod shell may be a straight cone (orthocone) as in the genus Orthoceras, or it may be a curved cone (cyrtocone) as in the genus Cyrtoceras. The cone may coil in one plane (planispiral), and is rarely trochospiral or irregular. The outer surface of the shell is ornamented by growth lines that show the different stages of the life history of the individual ontogeny. The edge of the shell is called the peristome.

Fig. VIII.3. General morphology of straight (A) and coiled (B) cephalopod shells (http://en.wikipedia.org/wiki/Cephalopod).

Description of shell The cephalopod shell can be easily oriented in the case of non-coiled shells. The ventral side is distinguished easily by the presence of a hyponome, which is always located in the abdominal area. The siphuncle is mostly located in the ventral side.

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The straight conical shell (orthocone) is described as a longicone or brevicone. The shells are described as cyrtocone if the curved cones do not complete a full circle. The majority of planispiral shells are bilaterally symmetrical. The umbilicus is present in the center. A shell with a wide umbilicus is called evolute, and that with narrow umbilicus with the last whorl covering the previous whorls is involute. Forms of curved and straight cephalopod shells are illustrated in Figs. VIII.4 and VIII.5.

Fig. VIII.4. Shell forms of the curved cephalopod shells (http://en.wikipedia.org/wiki/Cephalopod).

Fig. VIII.5. Shell forms of the straight cephalopod shells (http://en.wikipedia.org/wiki/Cephalopod).

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Homeomorphy Homeomorphy in cephalopods is a phenomenon in which shells may be similar in their external features while different in their internal structures and morphological features. This phenomenon is common in cephalopods, which means that the shape of the shell is not important in classification and phylogeny. Septa and Sutures The shell cone is subdivided by septa. The septa are calcareous walls with a concavity toward the aperture (adorally). The siphuncle passes through the septa in an opening called the septal foramen. Each septum meets with the shell wall along a line called the suture line, which can be easily detected in the internal molds. The suture line may be simple or complicated (Figs. VIII.6 to VIII.11).

Fig. VIII.6. Major suture types of cephalopods (http://en.wikipedia.org/wiki/Cephalopod).

Function of the septa The septa give better resistance to the cephalopod shell because cephalopods live in a body of water, and travel through their life journey at varying depths, and thus are subject to an external hydrostatic pressure. The septa in the presence of siphuncle treat the problem of the external hydrostatic pressure by adjusting the gas inside or outside chambers to offset these pressures. The winding of a suture line means that the edge of the septum also winds, and thus the degree of docking with the inside wall of a shell is large, which means strengthening the docking therefore increasing resistance. This means that such cephalopods with complex sutures had the ability for vertical movement faster in the water body, up and down.

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Fig. VIII.7. Morphology and types of suture lines in Ammonites (http://en.wikipedia.org/wiki/Cephalopod).

In suture lines with sinusoidal folds, the deflections directed toward the top are called a lobe, and those directed toward the aperture are called a saddle. The lobes and saddles may be sinusoidal formed secondary lobes and saddles (subsidiary). Because the suture lines are very diverse and complex, they have importance in the cephalopod classification. In spite of the fact that the suture lines surround the shells completely, they are put in the linear form when drawn (Fig. VIII.6). Usually one draws a half suture line from the mid-side (mid-venter) to the mid-dorsal side (mid-dorsal). The middle ventral is referred to arrow up. Types of sutures The following are the five types of suture lines in Cephalopoda and especially in Ammonites (Figs. VIII.6 to VIII.11), as it is the most important taxonomic group of class Cephalopoda: 1.

Orthoceratitic suture: It is characterized by no lobes or saddles, except broad wind – if any – or round lobes and saddles (Fig. VIII.8). This type is found since the Paleozoic to the Recent.

Fig. VIII.8. Orthoceratitic suture.

2.

Agoniatitic suture: It consists of a few simple undivided lobes and saddles (Fig. VIII.9). This type distinguishes the cephalopods of the Early and Middle Devonian.

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Fig. VIII.9. Agoniatitic suture.

3.

Goniatitis suture: Numerous undivided lobes and saddles; typically eight lobes around the conch (Fig. VIII.10). This pattern is a characteristic of the Paleozoic ammonoids. Cephalopods with goniatitis sutures are called goniatits.

Fig. VIII.10. Goniatitis suture.

4.

Ceratitic suture: It is characterized by rounded and undivided saddles and serrated lobes (Fig. VIII.11). The most ceratitic sutures characterize the Triassic and some of the Cretaceous cephalopods. The cephalopods with ceratitic sutures are called ceratites.

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Fig. VIII.11. Ceratitic suture.

5.

Ammonitic suture: It is characterized by serrated lobes and saddles (Fig. VIII.12). It is most common in the Jurassic and Cretaceous periods. Cephalopods with ammonitic sutures are called ammonites.

Fig. VIII.12. Ammonitic suture.

Siphuncle The siphuncle is a unique organ in the cephalopoda. It consists of soft and solid parts. In the genus Nautilus, the soft parts include blood vessels, nerves and the mantle. The non-living part of the siphuncle is called ectosiphuncle. The ectosiphuncle consists of a tube that extends from the top to the body chamber, and consists of a septal neck and a connecting ring (Fig. VIII.13).

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In many fossils, there are deposits on the walls of chambers called cameral deposits. These deposits are important in the classification of some cephalopods. They functionally help in effective positive bouncy in shells that are filled with gases, especially in conical and curved shells.

Fig. VIII.13. Siphuncle in a cephalopod shell (http://en.wikipedia.org/wiki/Cephalopod).

Classification The Cephalopoda are classified into six subclasses, including at least 26 orders. Five of these subclasses are characterized by the presence of external shells, and the last one possesses internal shells or no shells at all. 1. Subclass Nautiloidea They are cephalopods with external shells, small to large, straight conical or planispiral, with bilateral symmetry, rarely twisted and thus losing their bilateral symmetry. Suture lines are straight simple in general, and lobes and saddles are few. The siphuncle is usually peripheral, and the diameter is not large and takes ventral to below dorsal positions. The siphuncle neck twists against the top. Connecting rings are thin or thick. Cameral deposits are common in non-coiled shells. From late Cambrian to Recent, it includes 700 genera. 2. Subclass Endoceratoidae They are cephalopods with external shells, middle to large in size, mostly straight conical, and rarely inclined conical. Suture lines are simple straight, and sometimes include a middle ventral lobe or saddle. The siphuncle has a large diameter (half the diameter of the shell), peripheral to sub-peripheral and mid-ventral in most species. The septal neck twists towards the top. Connecting rings are thin or thick, and the cameral deposits are not present. From late Cambrian or early Ordovician to Silurian (extinct subclass), it includes at least 80 genera. 3. Subclass Actinoceratoidea They are cephalopods with external shells, middle to large, mostly straight conical, and rarely inclined conical. Suture lines are simple ceratitic, and the cameral deposits are common. The siphuncle neck twists against the top. Connecting rings are complicated. The body whorl has a contracted aperture. The siphuncle is usually of large diameter and may occupy half the diameter of the body whorl, peripheral to sub-central and ventral. The siphuncle has internal deposits. From late Cambrian or middle Ordovician to late Mississippian (extinct subclass), it includes at least 40 genera.

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4. Subclass Bacteritoidea They are cephalopods with external shells, small in size, thin, straight conical or inclined, and exogastric. Suture lines are simple orthoceratitic with a mid-ventral lobe. The siphuncle neck twists against the top. Cameral deposits and siphuncle deposits are not present. The siphuncle is small, peripheral to sub-peripheral and ventral. Protoconch is small, mostly spherical and contrac when it connects with the shell. From Devonian to late Triassic (extinct subclass), it includes at least 30 genera. 5. Subclass Ammonoidea They are cephalopods with external shells, small or large, nearly coiled in planispiral types, and mostly anticline ventrally. It has suture lines of agonitites, goniatets, ceratites and ammonites types. The siphuncle neck usually twists toward the top in the adult stage. Cameral deposits are not present. The siphuncle is mostly peripheral with a small diameter, taking the abdominalay location and rarely taking the dorsal position. From early Devonian to late Cretaceous, it includes 2000 genera. 6. Subclass Coleoidea They are cephalopods that are mostly with internal or without shells, small to very large in size. The shell is of straight conical or inclined and is rarely coiled. The mantle covers the whorl body. From early Devonian to Recent, it includes 250 genera. Order Belemnitidea from late Mississippian to late Cretaceous is the most important fossil group of this subclass. Dimorphism in the Cephalopods The sexes are separate in cephalopods. In the genus Nautilus, there are differences between male and female concerning shell shape, size and the shape of the aperture. Paleontologists indicated that ammonite shells may be present in two morphological groups in the same bed: One with a highly ornamented, tightly coiled and small shell (microconch), and the other with low ornamentation, non-tightly coiled and large shell (macroconch). Ecology and Mode of Life It seems that the cephalopod fossils were swimmers like their modern representatives. This explains the wide geographical distribution across the world. When members of the genus Nautilus die, their shells float due to the decomposition of soft tissues. Currents distribute the shells in the Indian Ocean, and western Pacific far from their origin. Modern cephalopods live in shallow marine coastal areas. The genus Nautilus is present today in the southwest Pacific as well as in the tropics at a depth range of 5-550 meters. It may be present along the eastern coast of Africa. It is an active swimmer and sometimes inserts itself in the bottom sediments through the tentacles. This method is called nekton-benthonic. Cephalopoda with 10 tentacles are found in the oceans of the world and include the largest invertebrate predators. They live at depths from the surface to not more than 300 meters. Modern squids swim in large groups in an open marine environment and near the beach. Cephalopoda with eight tentacles such as the octopus live nearly in all seas. Their types are mostly found in shallow marine waters. The deep types are present around 500 meters in depth.

Class Cephalopoda

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Questions on Class Cephalopoda 1st Question: Choose the correct answer 1. 2. 3.

4.

5.

Cephalopods are: a) all marine


The basic shell shape in Cephalopoda is: a) bivalved b) hollow conical Cephalopods are: a) benthonic sessile d) nekton

b) benthonic vagile

The stratigraphic range of Cephalopoda extends from: a) Ordovician to Recent b) Cambrian – Recent d) Cambrian – Cretaceous Cephalopoda are: a) filter feeders

b) Herbivores

6.

Suture line in Cephalopods is: a) the intersection of septa with the inner surface of the shell b) the line separating two successive whorls

7.

The living animal in Cephalopods lives in: a) the last chamber b) the last whorl

8.

Cephalopod shells are: a) coiled

9.

b) non-coiled

Most Cephalopod shells are: a) coiled planispiral b) coiled trochospiral

c) mostly aquatic, few terrestrial c) septate conical c) benthonic sessile & vagile


c) Carnivores

c) both c) non-coiled

10. Symmetry in Cephalopods is: a) bilateral b) radial

c) non-symmetrical

11. Suture line characterized by no lobes or saddles: a) Orthoceratitic b) Agoniatitic

c) Goniatitic

12. Suture line consists of few simple undivided lobes and saddles: a) Orthoceratitic b) Agoniatitic

c) Goniatitic

13. Suture line is characterized by rounded and undivided saddles, and serrated lobes: a) Ammonitic b) Ceratitic c) Goniatitic 14. Suture line characterized by serrated lobes and saddles: a) Ammonitic b) Agoniatitic

c) Goniatitic

2nd Question: Give the scientific term to the following definitions 1. 2.

Cephalopod shells are similar in their external features, while different in their internal structures and morphological features. Suture line is characterized by no lobes or saddles.


74 3. 4. 5.

Suture line consists of few simple undivided lobes and saddles. Suture line is characterized by rounded and undivided saddles, and serrated lobes. Suture line is characterized by serrated lobes and saddles.

3rd Question: Complete 1. 2. 3. 4. 5. 6. 7. 8.

The stratigraphic range of cephalopods is …………… The function(s) of septa in cephalopods …………… The cephalopod shell is divided into two parts: …………… and …………… A shell with a wide umbilicus is called ……………, and that with a narrow umbilicus is …………… The siphuncle passes through the septa in an opening called …………… Each septum meets with the shell wall along a line called …………… In a suture line, the deflections directed toward the top are called ……………, and those directed toward the aperture are called …………… The Cephalopoda have five types of suture lines: ……………, ……………, ……………, …………… and ……………


The shape of cephalopod shells is not important in classification and phylogeny. The presence of suture lines in cephalopods.

5th Question: Write down on the following 1. 2. 3. 4.

Homeomorphy Function of the septa Types and functions of suture lines Dimorphism in cephalopods

6th Question: Label

Class Cephalopoda

7th Question: Write the type of the suture line

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CHAPTER IX

CLASS PELECYPODA

Objectives 1. 2. 3. 4. 5. 6. 7. 8.

Define pallial line, ligament and beak. State the basis of bivalve classification. List the types of adductor muscle scars. Compare between different types of bivalve dentations. List the type of the dentition of pelecypods. Describe the mode of life of pelecypods. Interpret the paleoecology using bivalve fossils. List the type of gills in pelecypods. Overview

Bivalves secrete bivalved shells, mostly equivalved (Fig. IX. 1), inequilateral (mostly), and of bilateral symmetry. Calcareous shells of calcite or aragonite or both together. The shell consists of two valves and includes soft tissues. In contrast to brachiopods, bivalves are more common and diverse in modern times. Nearly all coastal areas include remains of pelecypods worldwide. Pelecypods are aquatic, mostly marine, sessile, epifaunal or infaunal. Some inhabit fresh water. Recorded in the early Devonian and increased in the Mesozoic era. Since the early Tertiary bivalves dominate over other shallow marine organisms. Anatomy The pelecypod shell is secreted by the mantle. On the pallial edge, there are three folds; the external one responsible for shell secretion, the middle is sensory, and the inner one is muscular. Within the shell (Fig. IX.1), the soft parts occupy the upper part, while the pallial cavity occupies the lower part. The mouth is towards the anterior and the anus towards the posterior ends in the pallial cavity. The large central foot is the dorsal organ used in digging the path of the animal in the sea floor. Along the two sides of the foot, the soft gills hang within pallial sinus. Near the mouth a pair of labial palls is found which is used with gills for feeding purposes. Morphology The pelecypod shell is composed of two valves, one on the right and the other is on the left. The two valves connect through a hinge, which is formed of teeth and sockets (Fig. IX.2). The two valves open and close using muscles and a ligament in addition to hinge. Bivalve shells are described as equilateral when their anterior and posterior parts are equal. They are also described as equivalve when their right and left valves are equal. The plane of symmetry is located between the two valves. 77

78


Shell length is from the anterior margin to the posterior one. Shell height is the largest distance normal to the length, from the beak to the ventral margin. Shell thickness is the largest distance normal to the plane of commissure.

Fig. IX.1. Internal anatomy of a pelecypod shell (http://en.wikipedia.org/wiki/Bivalvia).

Hinge and teeth A broad area under the umbo carries teeth separated by sockets (Figs. IX.2 and IX.3). Each tooth in one valve meets with a socket in the other valve. The functions of the hinge are to control the opening and closing of the two valves and to prevent the slip of one to the other. Dentition in bivalves is very important in identification and taxonomy. There are many types of dentition:       

Heterodont: Having the cardinal and lateral teeth either in front and/or behind the beak (Fig. IX.2A). The cardinal teeth are the teeth immediately below the beak. The lateral teeth are the teeth extending laterally from the beak. Taxodont: A series of small parallel to sub parallel teeth which are perpendicular to the hinge line (Fig. IX.2B) such as the genera Arca and Glycyimeris of modern pelycypods and genera Nucula and Praeleda of old pelycypods (Paleotaxodont). Isodont: Very large teeth, symmetrical around the resulium (Fig. IX.2C) such as the genus Spondylus. Also may be very small as in the genus Pecten. Dysodont: Small teeth, close to the valve edge such in the genus Mytilus (Fig. IX.2D). Schisodont: Having prominent bifurcating or diverging teeth. Exclusive for the family trigoniacea with very large teeth, three in the left valve and two in the right one such the genus Trigonia (Fig. IX.2E). Desmodont: Teeth reduced or absent, replaced by some ridges on the hinge line such in the genus Mya. All desmodont bivalves are infaunal and fiter-feeder. Pachydont: Very large, heavy and hard teeth (Fig. IX.2F), only in the Rudiesta group where the shell is fixed by the large and heavy left valve, while the right one is a delicate valve.

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Fig. IX.2. Dentitions in pelecypods. (A) Heterodont. (B) Taxodont. (C) Isodond. (D) Dysodont. (E) Schisodont. (F) Pachydont.

Ligament The ligament is made from organic horny material that connects the two valves of the shell during opening and is rarely fossilized. It has three positions (Fig. IX.4):   

Opithodetic: Located in an elongate pit behind the umbo and above the hinge line (Fig. IX.4A) as in the genera Cardita and Circe. Amphidetic: Located above the hinge line and in anterior and posterior sides (Fig. IX.4B) such as in the genera Anadara and Glycemeris. Resilum: Located as triangular pit with isodont teeth (Fig. IX.4C) such as in the genera Spondylus and Pecten.

Adductor muscle scars Muscles help by their contraction and relaxation with the ligament in opening and closing the bivalve shell. The scar of a muscle is shown in the internal surface as an ovate, smooth area. The following are examples of adductor muscles scars (Fig. IX.5): 

Dimyrian: A valve has one anterior and one posterior adductor muscle scar. There are two types of dimyrian: - Isomyrian: A dimyrian shell where two adductor scars are equal in size (Fig. IX.5A) as in the genera Glycemeris and Cerastoderma.


80 

Anisomyrian: Dimyrian shell where the two adductors are unequal in size (Fig. IX.3), usually the posterior scar is the larger as in the genera Dosinia and Mytilus. Monomyrian: A shell has only one adductor scar (Fig. IX.4C), which is usually central in position towards the posterior as in the genera Pecten and Spondylus.

Fig. IX.3. Morphology of the internal and exterior pelecypods (http://en.wikipedia.org/wiki/Bivalvia).

Pallial line The line of mantle attachment, connects between the two adductor muscle scars and parallel to the ventral edge. The pallial sinus is an indentation in the posterior part of the pallial line where the siphons can be retracted.  

Integripalliate: When the pallial line is complete as in the genus Anadara (Fig. IX.4B). Sinopalliate: When a sinus is formed in the posterior edge of the shell (Fig. IX.3) due to the contraction of the two siphons as in the genera Dosinia and Mya.

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81

Fig. IX.4. Positions of ligament in pelecypods. (A) Opithodetic. (B) Amphidetic. (C) Resilum.

Beak The beak is the region of the initial growth of the shell. The general region of the beak is often called the umbo. There are three main types (Fig. IX.5):   

Orthogyral: Beak straight, not inclined to any side as in the genus Glycymeris (Fig. IX.5A). Prosogyral: Beak is inclined towards the anterior side (Fig. IX.5B) due to an increase in shell growth in the posterior side faster than the anterior one as in the genus Cardita. Opisthogyral: Beak is inclined towards the posterior side (Fig. IX.5C) due to an increase shell growth in the anterior side faster than the posterior one as in the genus Ostrea.

Ornamentation The external surface of the bivalve shell is covered by different ornamentations which may be (Fig. IX.6):  



Concentric growth lines as in the genus Lucina (Fig. IX.6A). Radial ribs extending from the umbo on the dorsal side to the ventral side. Radial ribs may be numerous as in the genus Anadara (Fig. IX.6B) or few and strong as in the genus Tridacna. Also they may be smooth or with granules or scales as in the genus Chlamys (Fig. IX.6C) or carry spines as in the genus Spondylus (Fig. IX.6D). Reticulated when the radial ornamentation meets with concentric ones (Fig. IX.6E) as in the genus Barbatia.

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Fig. IX.5. Positions of beak in the pelecypods. (A) Orthogyral. (B) Prosogyral. (C) Opisthogyral.

Fig. IX.6. Different ornamentations of pelecypods shells. (A) Concentric growth lines. (B) Radial ribs. (C) Scales. (D) Spines. (E) Reticulate.

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83

Shell Microstructure and Mineralogy The bivalve shell is multilayered consisting of two stages: 1. 2.

Organic matrix. Crystallized calcium carbonate in the form of calcite or aragonite. Some such as Oysters of calcite only and others of aragonite, but most of calcite and aragonite together in the same shell. Six structures can be distinguished and they are as follows (Fig. IX.7):  Simple prismatic: Composed of multi-faced calcite or aragonite pillars.  Composite prismatic: Characterized by very minute needle-like, radial crystals.  Nacreous: Disc plates of aragonite. Usually are present in the middle or external layer of a shell.  Foliated: Composed of small calcite crystals, arranged in successive plates.  Crossed-lamellar: Composed of aragonite, usually in several lamellae. In each lamella, aragonite crystals arrange in different positions to the neighboring one.  Homogenous: Composed of very small, granular-shaped, without crystal faces.

Fig. IX.7. Shell microstructure of pelecypod walls (Clarkson, 1994).

Gill morphology In spite of their importance in bivalve taxonomy, gills do not preserve as fossils. They hang within mantle cavity. There are four types of gills:    

Protobranch: Small and leaf-like in shape as in crystals order Nuculoida (Ordovician to Recent). Filibranch: Composed of lamellar plates, W-shaped. Eulamellibranch: Resemble filibranch but are provided with a transverse septa as in Cardium edula. Septibranch: Exclusive in the superfamily Poromyacea (boring in hard rocks). They are present transversally in the pallial cavity. Mode of Life

Free active Most pelecypods live free active using their foot which contracts and relaxes on the sea floor. Burial in soft sediments takes place in the same manner. This type of movement is common in Herterodonta (Anomalodesmata). Shells are usually equivalved and isomyrian (or anisomyrian) with a distinct pallial line. They include the nuculoid burrowing deposit feeders, the shallow burrowing non-siphonate forms lacking a pallial sinus, and deep burrowing siphonate forms identified by a distinct pallial sinus (Fig. IX.8).

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Fig. IX.8. Burrowing pelecypods in soft sediments (http://en.wikipedia.org/wiki/Bivalvia).

Boring pelecypods Boring pelecypods of the genus Pholas fix themselves on a hard substratum by suction and by the anterior part of the shell pore substratum. Other poring pelecypods such as the genera Lithophaga and Hiatella secrete acids by a special gland in the mantle which dissolves the substratum of calcium carbonate (Fig. IX.9). Shells are usually thick, equivalved, and cylindrical in cross section. Some forms are moderately ornamented with ridges and stout spines, whereas others such as the “ship worms” are tubular in form.

Fig. IX.9. Boring Lithophaga in corals (http://en.wikipedia.org/wiki/Bivalvia).

Free swimming A few pelecypods are able to swim (Fig. IX.10). They mostly close their valves fastly, then quickly expel water from their mantle cavity and consequently the shell moves straight forward. The shells are usually equilateral but not equivalved. The lower (usually the left) valve is usually slightly larger. Swimming forms are typified by having a greater umbonal angle (greater than 105°) than similar-looking

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85

epibyssate forms. Furthermore, swimming forms typically have a single (monomyrian), large, centrally located adductor muscle.

Fig. IX.10. Examples of free swimming pelecypods. (A) Genus Pecten. (B) Genus Chlamys.

Fixed pelecypods Fixed by byssus The byssus may continue with the shell through its life as in pteriomorphs. Heterodonts mostly use a byssus in early stages then choose a hard substratum to fix upon. Some byssate forms such as Mytilus may change its position by the breakdown of byssus threads and use its foot to change position and then secrete a new byssus (Fig. IX.11). Also the genus Chlamys may change position by swimming. Fixed by shell Some pelecypods directly fix themselves by their shell such as modern oysters. The fixed valve takes substratum-shape and the other valve takes the same edge of the fixed valve to be tight closing. Many are fixed by shell pelecypods build reef/refoid buildups such as rudusts (hippuritids) of cone shape in Cretaceous rocks of Abu Roash and Sinai, Egypt (Fig. IX.12). Classification The classification of Bivalvia depends on shell microstructure, dentition, hinge structure, gill morphology, stomach anatomy and the nature of the labial palps. Accordingly, the bivalvia is classified into five subclasses (Moore, 1969). Subclass paleotaxodonta Shell small, equivalve, inequilateral, composed of aragonite, internal layer usually nacreous, beak prosogyral or opithogyral, few semi-orthogyral, taxodont, ligament mostly internal (reselium), amphidetic, few opithodetic, symmetric dimyaria, some with reduced posterior muscle or absent, mostly integripalliate, sometimes sinupalliate, living types with protobranch, without byssus, all marine, infaunal, from subtidal to more than 5000 m depth. From Cambrian to Recent, the subclass includes 150 genera and 500 living species.

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Fig. IX.11. Examples of pelecypods fixed by byssus. (A) Genus Mytilus. (B) Genus Tridacna.

Subclass Sofilibranchia Shell equivalve, mostly inequilateral, composed of aragonite, or calcite and aragonite, byssus absent, beak prosogyral or orthogyral, hinge with one or more small teeth of semi-taxodont, mostly symmetric dimyaria, a few with posterior muscle, siphonal canals absent, integripalliate, worm-tube foot, filibranch, mostly marine, some inhabit brackish water, few in fresh water, mostly live on the sea floor byssate some boring into rocks. From early Cambrian to Recent, the subclass includes 140 genera and 250 living species. Subclass Heteroconchia Shell of variable size, equivalve, inequilateral, composed usually of aragonite, without byssus, beak prosogyral, mostly heterodont, few taxodont, hinge plate mostly present, ligament mostly opithodetic, some with reselium, mostly symmetric dimyaria, some with asymmetric dimyaria, sinpalliate or integripalliate, siphonal canals mostly present, mostly with boring foot, mostly with eulamellibranch, some of filibranch, mostly marine, include most of fresh water pelycypods, some live in swamps, few terrestrial, mostly boring, filter feeder, mostly prefer shallow water, some with tide zone, few reach 4800 m depth. Subclass Pteriomorpha Sell of variable size, composed of aragonite or calcite or both, mostly inequivalve, beak variable, some orthogyrate, mostly byssate, dentition variable, heterodont, taxodont others, some fixed, ligament amphidetic, opithodetic, few reselium, asymmetric dimyaria common, symmetric dimyaria and monomyaria present, foot reduced in some and absent in others, siphonal canals absent, mostly with filibranch, some with eulamellibranch, mostly marine, some live in estuarine, few inhabit fresh water, mostly epifaunal, byssate, some boring, some swimmers, all filter feeder, inhabit within tide zone and shallow water, few present in deep water. From early Ordovician to Recent, the subclass includes 90 genera and 1200 species.

Class Pelecypoda

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Fig. IX.12. Examples of fixed by shell pelecypods. (A) Genus Durania. (B) Enlargement of the same. (C) Genus Exogyra. (D) Genus Ostrea.

Subclass Anomalodesmata Shell short to elongate, composed of aragonite, primitive types equivalve, internal and prismatic layers nacreous, few byssate, ligament opithodetic, mostly symmetric dimyaria, rarely asymmetric dimyaria, desmodont, siphonal canals mostly present, developed foot, eulamellibranch or absent, all marine, mostly boring, semi-burial, fixed, filter-feeder, some predators, from shallow to deep marine water. From Ordovician to Recent, the subclass includes 100 genera and 400 species.


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Questions on Class Pelecypoda 1st Question: Choose the correct answer 1. 2.

3.

4.

5. 6. 7. 8. 9.

Pelecypods are: a) all marine Pelecypods are: a) benthonic sessile d) benthonic & nekton


c) mostly aquatic, few terrestrial

b) benthonic vagile


The stratigraphic range of Bivalvia extends from: a) Ordovician to Recent b) Cambrian – Recent d) Cambrian – Cretaceous


Pelecypods are: a) filter feeders d) all options

b) Herbivores

c) Carnivores

b) diductors

c) oblique

Muscles in pelecypods are: a) adductors

The most common type of dentition in pelecypod is: a) taxodont b) heterodont

c) isodont

Rudists have dentition of the type: a) pachydont b) taxodont

c) desmodont

Pelecypod shells consist of: a) calcite

c) both

b) aragonit

Beak in most pelecypods are directed: a) anteriorly b) posteriorly

10. The most common type of gills in class Bivalvia is: a) filibranch b) eulamellibranch

c) orthogyral c) septibranch

11. In pelecypods, teeth & sockets present in: a) both valves b) teeth in one valve and sockets in pedicle one 12. The anterior muscle is: a) larger than posterior one

b) smaller than posterior one

13. The mode of life of pelecypods is: a) fixed by shell or byssus b) free swimmer d) all options

c) equal to posterior one c) boring or burrowing


An organ occupies the bulk of the mantle cavity used for gathering food, respiration and filtration. A long bar-like loop (tie shoe) organ that supports the lophophore. A triangular area located between the pedicle foramen and the umbo of the brachial valve. Many brachiopods are similar in external features and differ in their internal ones.

Class Pelecypoda

3rd Question: Complete 1. 2. 3. 4. 5. 6.

The functions of mantle in Bivalvia are …………… The function dentition in pelecypods is …………… The functions of siphons in Bivalvia are …………… The functions of ligament in Bivalvia are …………… The functions of muscles in Bivalvia are …………… The stratigraphic range of Pelecypods is ……………

4th Question: Justify 1. 2. 3. 4. 5.

Rudists have one very thick valve and the second is much smaller. Oysters of the same species may have different shapes and dimensions. The posterior muscle is larger than the anterior one. Boring pelecypods have pronounced sculpture. Burrowing pelecypods have smooth sculpture.

5th Question: Label

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CHAPTER X

PHYLUM BRACHIOPODA

Objectives 1. 2. 3. 4. 5. 6. 7.

List the functions of the lophophore. Define the homeomorphy. Compare between articulata and inarticulata. State the most environmental parameters affecting brachiopods ecology. Discuss the geologic history of brachiopoda. Differentiate between brachiopods and bivalves. List the modes of life of the brachiopods. Overview

Marine invertebrates, with two inequivalved and equilateral shell, hinged at the rear end. The pedicle may project from an opening in the pedicle valve, attaching the animal to the seabed. They mostly live on continental shelves and the upper parts of continental slopes. From Cambrian to Recent. Morphology Soft parts Internal surface of the shell is entirely bounded by epithelium. It is divided into the body cavity in posterior part and the mantle cavity in anterior part, and separated by the anterior body wall. The alimentary canal (Fig. X.1) consists of the mouth, followed by the esophagus, stomach, and then the intestine (blocked in articulate brachiopods, or end by anus in inarticulate brachiopods). The pedicle is a soft part, emits from the pedicle valve (pedicle foramen) to fix some brachiopods on the substratum. The pedicle may be solid or fibrous, as in the class Articulata, and may be hollow as in the class Inarticulate. It may be long flexible as in the genus Lingula (Fig. X.5). The pedicle is an important basis for brachiopod classification. There are three types of muscles (Ruppert et al., 2004) that are different in types and functions and have a role in brachiopod classification: adductors, diductors and oblique. The function of adductors and diductors in articulate brachiopods is close and open shell respectively, where they work in an opposite manner (Figs. X.1 and X.3). The number of muscles is abundant in inarticulate brachiopods and includes adductors and oblique muscles. Lophophore is a fleshy hollow hair which is a provider of cilia and occupies the bulk of the mantle cavity. It extends in front as two wrapped hands in reverse of each other; one of them is called the arm or brachia. The functions of lophophore are: pumping water into the shell, and filter of food and breathing (Doherty, 2001).

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Fig. X.1. Morphology of soft parts (Modified after Clarkson, 1979).

Hard parts Inside the shell The shell from the inside includes (Figs. X.2, X.3 and X.5) articulation, brachidium and muscle scars. The articulation device consists of two teeth in the pedicle valve and two sockets in the brachial valve. The function of articulation is linking the two valves with the ability to move (hinge). The line that goes through the teeth and cavities is called the hinge axis. Brachidium is a long bar-like loop (tie shoe) that supports the lophophore.

Fig. X.2. Location of teeth and sockets in an orthide brachiopod (Rowell and Grant, 1987).

Outer surface of the shell The morphological features of the shell (Figs. X.4 and X.5) consist of the umbo, pedicle foramen, delthyrium, commissure line and ornamentation. The umbo is in the posterior part of the shell and represents the embryonic stage. It may be straight or twisted. The pedicle foramen is present in the posterior part of the pedicle valve. It is often circular, small or large, or may not exist when the pedicle is absent.

Phylum Brachiopoda

93

The delthyrium area is a triangular area located between the pedicle foramen and the umbo of the brachial valve. This area represents the distance the pedicle foramen cut during the life of the individual. The basic types of ornamentation are growth lines, radial ribs, and network with short or long spines. Shell Description and Orientation The shell is composed of two equilateral and unequal valves (Fig. X.4). One valve is large and is called the pedicle valve (= dorsal valve). The other is small and is called the brachial valve (= ventral valve). Most brachiopod shells are biconvex. They also may be plano-convex and concavo-convex (Fig. X.6). The anterior part of the shell is the part where it opens and the posterior one is the part where the two valves hinge. The dimensions of the shell are the length, width and thickness. The line of symmetry is perpendicular to the commeasure line between the two valves.

Fig. X.3. Closing (A) and opening (B) of valves of a typical hinged brachiopod (Rowell and Grant, 1987).

Fig. X.4. General morphology of a brachiopod shell (http://en.wikipedia.org/wiki/Brachiopod).

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Fig. X.5. External and internal morphology of genus Magellanea (Clarkson, 1979).

Phylum Brachiopoda

95

Fig. X.6. Different shapes of brachiopod shells (http://en.wikipedia.org/wiki/Brachiopod).

Shell Composition and Structures Most brachiopod shells consist of calcite. This explains their good preservation from the Cambrian period. However, a small group of inarticulate brachiopods consist of aragonite. Most of the inarticulate ones have phosphate shells (apatite). These shells are originally Chitino-phosphatic and consist of alternating layers of chitin and phosphate, but the chitin dissolve after fossilization and such shells become phosphate only. The calcareous shells as in all articulata consist of two layers: An external organic layer called the periostracum, and an internal one of calcite, which consists of several chips and has several structures (Fig. X.7): 1. 2. 3.

Impunctate: A solid layer that does not have perforations. Punctate: Perforated layer. Pseudopunctate: With pseudo perforations. Homeomorphy

Many brachiopods are similar in external features and differ in their internal ones. These homeomorphic shells belong to different types and sometimes genera and families. For example, the genus Composita of order Spiriferida is similar to many genera of the order Terebratulida in their external features. Isochronous homeomorphs have the same age, while heterochronous homeomorphs have different age. As a result of spreading of this phenomenon among brachiopods, the definition of morphologically similar species need a series of successive serial sectioning to know the internal structures, particularly the calcifying Brachidium.

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A = impunctate, B = pseudopunctate, C = punctate Fig. X.7. Shell structures of calcareous brachiopod shells (Moore et al., 1953).

Classification According to shell composition (calcareous, Chitinophosphatic, chitinous), articulation (with or without), pedicle (present, reduced or absent), gut (with or without anus), the phylum brachiopoda is classified into three classes. Class Articulata Brachiopods with valves articulated by a hinge, consisting of teeth in the pedicle valve and sockets in the brachial valve. The shells are entirely of calcite. The pedicle consists of a dead substance, and it is often a solid or fibrous. The intestine is blocked. This class is the most abundant and diverse class. It appeared in the early Cambrian and had its peak in diversity in the early Ordovician. It includes seven Orders in the Paleozoic Era, three of them still alive today. This class includes some 2300 genera. Class Inarticulata Brachiopods lack the presence of an articulation device. The shells of phosphate (apatite) and some of calcite and one group of aragonite. Oblique adductor muscles. Gut open and ends by an anus. The pedicle is hollow, and it may be absent or reduced. From early Cambrian to Recent, this class includes less than 200 genera. Class Lingulata It is like inarticulate brachiopods, but the shells are of chitin. From early Cambrian to Recent, this class includes 85 genera. Ecology Brachiopoda live in the marine environment, from the intertidal zone to the depths of the ocean. They are distributed geographically in the seas of the world. The most important environmental factors affected the presence of brachiopods are as follows.

Phylum Brachiopoda

97

1. Depth Most brachiopods inhabit the continental shelf and upper parts of the continental slope, in water depth less than 500 meters. The favorite depth is 100-200 meters. Species with wide geographical distribution live at depths exceeding 2000 meters. One species is recorded at a depth of 6179 meters in the South Atlantic. 2. Salinity In general, brachiopods are euryhaline, but the genera and species may be stenohaline. Most brachiopods live in normal marine salinity (35%). Some species show high flexibility concerning the salinity gradient, and can live in a salinity that fluctuates between 17-45%. 3. Water energy Energy of water (waves and currents) is important for sessile brachiopods as they bring in food, and remove their wastes. Avoiding high energy is essential for brachiopods fixed by a pedicle. High-energy currents or waves may remove fixation and turn over the free brachiopods. Most brachiopods inhabit depths between 100-200 meters, where water energy is high in depths less than 100 meters. Below 200 meters depth, light and productivity are limited and consequently the amount of food decreases. 4. Substrate and bottom sediments The hard substrate such as rock substrata or dead shells is preferable for most brachiopods. Spinose brachiopods need friable substrate such as loose sands. Boring brachiopods need soft substrates like mud and sand. Modes of Life The following are the different modes of life of brachiopods. 1. Pedicle attachment Brachiopods fixed themselves onto hard rocks and shells by their pedicle (Fig. X.8). Examples are: Rhynchonellida, Terebratulida, Spiriferida, Strophomenida, and Pentamerida. 2. Free lying It is believed that most of the Articulata that have no pedicle foramen such as Strophomenida, Strophomenida and Orthida lived lying on the seabed. They removed deposits close to the line of fusion of the two valves by the rapid closing of the valves. 3. Cemented The genus Crania of the inarticulata lives cemented to a solid rock surface by its pedicle valve. The shape of the pedicle valve depends on the shape of the substratum. 4. Semi-buried Articulate brachiopods of the orders Productida and Strophomenida lived buried in sediments, so that the sediment covered the brachial valve. The anterior part opens for a few minutes to allow food and water to enter the interior.

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5. Burrowing Brachiopods of becomes still class lingulata as becomes still genus Lingula lives in burrows in muddy sediments in the intertidal zone. The length of hole reaches about 10 centimeters. The pedicle is flexible, and fixes the brachiopod in the burrow floor.

Fig. X.8. Brachiopods fixed by pedicle on hard substratum (http://en.wikipedia.org/wiki/Brachiopod).

Geologic History The oldest brachiopods were found in the Cambrian period, and their fossil record is very rich, especially in shallow marine sediments. In the Paleozoic Era, they have three major diversity peaks in the middle Ordovician, Devonian and Permian. Brachiopods suffered greatly from the end of the Permian extinction, then re-emerged and spread slowly in the Mesozoic Era, but much less than the Paleozoic one (Fig. X.9). Also brachiopods suffered from the end Cretaceous extinction, so they almost become extinct. They reappeared again in the Cenozoic, therefore researchers think that brachiopods may be one of the extinct phyla.

Fig. X.9. Variation of brachiopod diversity with time represented by number of genera recorded from each geologic period (Rowell and Grant, 1987).

Phylum Brachiopoda

99

Questions on Phylum Brachiopoda 1st Question: Choose the correct answer 1. 2.

3.

4.

5.

6.

7.

Brachiopods are: a) all marine Brachiopods are: a) benthonic sessile d) benthonic & nekton

b) all aquatic mostly marine

c) few terrestrial

b) benthonic vagile


The stratigraphic range of brachiopods extends from: a) Ordovician to Recent b) Cambrian – Recent d) Cambrian – Cretaceous


Brachiopods are: a) filter feeders d) all options

c) Carnivores

b) Herbivores

Muscles in articulated bracgiopods are: a) adductors b) diductors d) 1 & 2 e) 1, 2 & 3

c) oblique

Muscles in inarticulated brachiopods are: a) adductors b) diductors d) 1 & 2 e) 1, 2 & 3

c) oblique

Brachiopoda are of: a) bilateral symmetry

b) bilateral and radial symmetry

c) asymmetrical

8.

The plan of symmetry in brachiopods passes: a) between the two valves b) normal to the surface between valves

9.

In brachiopods, teeth and sockets present in: a) both valves b) teeth in brachial valve and sockets in pedicle one c) teeth in pedicle valve and sockets in brachial one

10. Most brachiopods inhabit the marine environments: a) between 100-200 m b) between 0-200 m

c) between 0-7600 m

11. Brachiopods of class Articulata have shells consisting of: a) calcite b) chitin d) chitino-phosphatic

c) phosphatic

12. Brachiopods of class Inarticulata have shells consisting of: a) calcite b) chitin d) chitino-phosphatic

c) phosphatic

13. Brachiopods of class Lingulata have shells consisting of: a) calcite b) chitin d) chitino-phosphatic

c) phosphatic

14. The most diverse class of the phylum Brachiopoda: a) Articulata b) Inarticulata

c) Lingulata


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An organ occupies the bulk of the mantle cavity, used for gathering food, respiration and filtration. A long bar-like loop (tie shoe) organ that supports the lophophore. A triangular area located between the pedicle foramen and the umbo of the brachial valve. Many brachiopods are similar in external features and differ in their internal ones.

3rd Question: Complete 1. 2. 3. 4. 5. 6. 7. 8.

The function of pedicle in brachiopods is …………………………………………… The articulation in brachiopods consists of ………………… in the pedicle valve and ………………… in the brachial one. The functions of lophophore in brachiopods are …………………………………………… The function(s) of muscles in brachiopods …………………………………………… The stratigraphic range of brachiopods is …………………………………………… Pedicle foramen presents in the posterior part of the ………………… valve. Delthyrium is a triangular area locates between ………………… and ……………… of the brachial valve. The line of symmetry is perpendicular to the ……………………………………………

4th Question: Justify 1. 2. 3. 4. 5.

Muscles in articulated brachiopods are fewer than in inarticulated ones. Most brachiopods live between 100-200 m depth. Most brachiopod fossils are well preserved. The definition of morphologically similar species needs a series of successive serial sectioning. Researchers think that brachiopoda is one of the extinct phylum.

5th Question: Label

CHAPTER XI

PHYLUM BRYOZOA

Objectives 1. 2. 3. 4. 5. 6. 7.

Define ancesterula, lophophore, autozooids and avicularia. State the basis of bryozoan classification. List the types of bryozoans growth forms. Compare between erect flexible and erect rigid bryozoans. Describe the bryozoan growth forms and ecological parameters. Interpret the paleoecology using bryozoans. Identify polymorphism in bryozoans. Overview

Bryozoans are exclusively aquatic invertebrates, mostly marine, benthic, mostly sessile, though a few ones can move (vagile), all are epifaunal. It is the only phylum among the invertebrates in which all species consist of colonies. They are distributed geographically from the tropics to the polar regions. Bryozoans have external skeletons consisting mostly of calcite, a few have organic skeletons. Polymorphism is common among bryozoans species due to the different functions of their individuals. The colony (zoarium) consists of small size individuals (zooids). The first individual (ancestrula) is formed through a sexual reproduction, while the rest of the colony is formed through asexual budding. The normal individual (autozooid) has a ring of tentacles surrounding the mouth (Fig. XI.1), and a digestive canal (U-shaped) (Fig. XI.2). From the Ordovician to Recent. Zooidal Morphology Individuals of bryozoan colonies are different in morphology and function. Except the feeding individuals (autozooids), others are specialized in reproduction, breathing, ventilation, cleaning, defense, protection, strengthening, and communication between members. Autozooids Autozooids are the most common type in the colony (Ruppert et al., 2004). They have tentacles as a feeding device, surrounding the mouth for collection of food. The device is called a lophophore and sometimes shrinks into the body space and other times go outside the stem. The autozooids have a digestive canal, muscles, and a nervous system. Reproduction The majority of marine bryozoans colonies arise from sexual reproduction. Gametes begin to form in the mother colony. In most species, the fertilized egg remains in the embryonic stage of the larva inside a special room known as the chamber of fertilization (brood chamber). 101

102


Marine bryozoan larvae have cilia and are usually able to swim. Their life period is short, usually not more than hours. After the larvae choose a suitable substratum, they begin to form the first individual (ancestrula) (Fig. XI.3). They successively increase the number of individuals by budding from the first individual.

Fig. XI.1. Morphology of living bryozoans with ring of tentacles around their mouths (http://en.wikipedia.org/wiki/Bryozoa).

Zoarial Growth Forms Bryozoan colonies take the following growth forms. 1. Encrusting zoaria This consists of a single layer (Figs. XI.4 and XI.5) of individuals such as genus Membrinopora, or of several layers (Fig. XI.6) such as the genus Holoporella. This layer or layers attach onto hard substrates and sometimes onto delicate ones. 2. Erect zoaria These resemble a tree, fixed only on the substratum by its base. The connection with the substratum may be either by small sheet as Tremogastrina fourtaui, or by rootlets in soft sediments as in Margretta cereoides. Erect zoaria may be either flexible or rigid. In the erect flexible growth form (Fig. XI.7) the joint material which links between branches is an organic material, which allows branches to move freely as in Cellaria sinusa. Branches in the erect rigid growth form (Fig. XI.8) connect with calcified materials, which do not allow branches to move freely about the origin as in Tremogastrina fourtaui.

Phylum Bryozoa

103

Fig. XI.2. Section through the body wall and organs of a generalized bryozoans feeding zooid (Boardman and Cheetham, 1987).

104


Fig. XI.3. Ancestrula (arrow) and successive asexually produced zooids in an encrusting Recent colony (Boardman and Cheetham, 1987).

Fig. XI.4. Single layer of encrusting growth form on a hard substratum of a molluscan shell.

Phylum Bryozoa

Fig. XI.5. Enlargement under SEM of the same.

Fig. XI.6. Several layers of encrusting growth form on a substratum of plant stems.

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106


Fig. XI.7. Erect flexible growth form (Boardman and Cheetham, 1987).

Fig. XI.8. Erect rigid growth form (Boardman and Cheetham, 1987).

Phylum Bryozoa

107

3. Free living zoaria A limited group of bryozoans can move about on bottom sediments (Fig. XI.9). The majority have inverted cup-shape. Examples include Cupuladria nummulitophyla from the upper Eocene of Egypt.

Fig. XI.9. Locomotion in the free-living anascan Selenaria (Boardman and Cheetham, 1987).

Classification The Recent certified classification of the bryozoa recognizes three classes. Class Stenolaemata Calcified marine bryozoans, usually non-operculate, with an extensive fossil record. Zooids are cylindrical and elongated zooecia continuing to grow throughout the life of the colony and set at an angle to the direction of colony growth. Each polypide is surrounded by a membranous sac. Tentacle extrusion in living forms is brought about by a muscular action forcing the coelomic fluid into the proximal part of the zooid displacing the tentacles distally. It includes 750 genera. From Early Ordovician to Recent, this class includes the orders Cyclostomata, Cystoporata, Trepostomata, Cryptostomata and Fenstrata. Class Gymnolaemata Marine, occasionally brackish or fresh water bryozoans which may be calcified. Zooids are box-like or may form short cylinders. Their size is fixed early in development and their long axis coincides with the local direction of the growth of the zoarium. Zooids are connected by a funicular network. Lophophores are exerted by a muscular deformation of a part of body wall. It is strongly polymorphic. It includes 1050 genera. From the late Ordovician to Recent, this class includes two orders: Ctenostomata and Cheilostomata. Class Phylactolaemata Non-calcareous freshwater bryozoans. It is a zooid with a horseshoe-shaped lophophore. Modern species have wide, commonly intercontinental distributions apparently because their resistant statoblasts are easily transported by migratory birds. Phylactolaemata are unknown as fossils. It includes 10 genera. From late Tertiary to Recent. Zoarial Growth Forms and Ecology Stach (1936), Lagaaij and Gauthier (1965), and Schopf (1969) studied the relationship between zoarial growth forms and ecological parameters of an environment. In general, the main environmental factors affecting the distribution of bryozoan’s colonies are as follows.

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1. Substratum For bryozoans there are three types of substrates: hard substratum such as rock surfaces and living or dead shells which are preferable for most bryozoans in highly agitated water to remove muddy sediments. Firm substratum such leaves, and seaweed, and soft substrate such mud and sand for bryozoans with rootlets to fix themselves or free living bryozoans (Lunulites, Cupuladria). 2. Water energy and depth Most bryozoans occupy the continental shelf and the very shallow areas in it. In shallow, highly agitated water, it is difficult to find erect rigid colonies where they crush easily. On the contrary, flexible colonies adapted with such environment, where flexibility allow movement and avoid the risk of high water energy. There are rigid colonies of fenestrate form (Fig. XI.10) which allow water to pass through their pores and therefore live in highly agitated water. Schopf (1969) concluded that the number of encrusting colonies decreases with increasing depth, and on the contrary, the two erect types of colonies increase in numbers with depth (Fig. XI.11).

Fig. XI.10. Erect rigid growth form (fenestrate) that allows water to pass through the pores (http://en.wikipedia.org/wiki/Bryozoa).

3. Rates of sedimentation All epibenthic sessile organisms cannot live in an environment with a high rate of sedimentation, or at least in rates of deposition that exceed growth rates, as they will be buried alive in such an environments. Therefore, the free living bryozoans are among the most capable to live in environment with high rates of sedimentation such as in a delta. Such organisms have the ability to move as well as, their colonies are associated with private individuals to remove the falling sediment on them.

Phylum Bryozoa

Fig. XI.11. Bryozoan fossils in an Upper Ordovician oil shale, northern Estonia (http://en.wikipedia.org/wiki/Bryozoa).

109


110

Questions on Phylum Bryozoa 1st Question: Choose the correct answer 1. 2. 3. 4.

Bryozoan species are: a) all colonial

b) mostly colonial

c) all solitary

Bryozoan skeletons are: a) calcitic

b) aragonite

c) both

Bryozoans are: a) aquatic

b) marine


Mode of life in Bryozoa is: a) Plankton

b) Benthonic

c) Nekton

5.

Bryozoans are: a) sedentary b) free living c) mostly sedentary, a small group are free living

6.

Polymorphism in Bryozoans is: a) frequent b) rare

c) absent

The name of the first individual in Bryozoan colony is: a) Ancestrula b) Autozooid

c) Gonozooid

The name of the feeding individual in Bryozoan colony is: a) Ancestrula b) Autozooid

c) Gonozooid

7. 8. 9.

Bryozoans which tolerate environments with high rates of sedimentation have the colonial growth form: a) free living b) erect c) encrusting

10. Bryozoans which tolerate environments with high energy have the colonial growth form: a) erect rigid b) erect flexible c) encrusting 11. A type of growth form consists of layer(s) on hard/delicate substratum: a) encrusting b) erect rigid c) free living 12. A type of growth form like a tree with organic materials in the joints between branches: a) encrusting b) erect rigid c) erect flexible 13. A type of growth form like a tree with calcified materials in the joints between branches: a) encrusting b) erect rigid c) erect flexible 14. A type of growth form can move on bottom sediments: a) free living b) erect rigid

c) erect flexible

2nd Question: Give the scientific term to the following definitions 1. 2. 3.

A type of growth form consists of layer(s) on hard/delicate substratum. A type of growth form like a tree with organic materials in the joints between branches. A type of growth form like a tree with calcified materials in the joints between branches.

Phylum Bryozoa

4. 5. 6. 7.

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A type of growth form can move on bottom sediments. Feeding individuals of bryozoans. A device consists of tentacles surround the mouth for collection and pick up food. The first individual arise from sexual reproduction.

3rd Question: Complete 1. 2. 3. 4.

Bryozoan colonies take the following growth forms: ………………, ……………… and ……………… The majority of marine bryozoans colonies arise from ……………… reproduction. The functions of tentacles in Bryozoa ……………… The main environmental factors affecting the distribution of bryozoans are ………………, ……………… and ………………

4th Question: Label

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5th Question: Write the type of growth form

CHAPTER XII

PHYLUM ECHINODERMATA

Objectives 1. 2. 3. 4. 5. 6.

List the function of tube feet. State the functions of appendages. Compare between crinoids and echinoids. Discuss the modes of life of echinoids. Differentiate between regularia and irregularia. List the composition of water vascular system. Overview

Echinodermata is a medium-sized phylum, with radial symmetry based on five or multiples. The skeleton is made of calcareous plates or ossicles. The lower surface contains umbulacral grooves with delicate and free moving tube feet. This represents the outer parts of tubular water vascular system which controls the movement of these tube-feet. Most surfaces of echinodermata are characterized by spines, from which the name of the phylum is derived. Most echinoderms are marine and prefer water with normal salinity (35%), and in a depth range from the tide until the depths of the ocean. From the early Cambrian or even Proterozoic to Recent. It includes five modern classes and about 6000 living species. Morphology The body of most echinoderms (Fig. XII.1) can be subdivided into three main parts: 1. 2. 3.

Internal soft tissues which includes the coelomic cavity, digestive system, the water vascular system, glands and other living organs. A rigid or flexible skeleton, which protects the soft tissues. Specialized appendages, in the form of plates or ossicles used in locomotion, protection, feeding, or attachment. Anatomy

The mouth is usually central, located on one side of the body (Fig. XII.2), and leads to the digestive system, composed of the mouth, esophagus, stomach/digestive gland and the anus. Some fragile sea stars have no anus, and the waste material is expelled through the mouth.

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Fig. XII.1


Modern representatives of the phylum Echinodermata. (A) Sea urchin. (B) Star fish. (C) Sea lilly. (D) Brittle star. (E) Sea cucumber (http://en.wikipedia.org/wiki/Echinoderm).

Phylum Echinodermata

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Fig. XII.2. Internal and external morphology of an echinoid test (http://en.wikipedia.org/wiki/Echinoderm).

The water vascular system (Fig. XII.3) exists in most echinoderms and consists of:  

Circumoral ring: Surrounds the esophagus, usually connects to the stone canal, with an opening to the outside. If the opening is single, the stone canal is called a hydropore and in case of multiple openings, it is called madreporite. Five radial canals radiating from the circumoral ring. Each of them extends outside until the ampullacral area is reached (used in gathering food).

The water vascular system is described as “open” if the radial channels pass to the outside, through the skeleton at some point and extend to the bottom, under the ambulacral furrows to the outside plates. However, if the radial channels remain internal and send their branches outside through one hole or a pair of holes through the skeleton it is termed closed. The function of the ampullae is control the water pressure inside the tube feet. The functions of the tube feet are feeding, breathing, movement, and sensors for protection. Skeleton The skeleton in echinoderms is usually covered by ciliated epidermis called skin, which is the outer surface of the animal. The skeleton in echinoderms has two designs: The first is called the theca (also called calyx, test or desk). It consists of many overlapping plates, surrounding the body and protects its soft tissues. These plates may be either tight overlapping to form a rigid skeleton or slowly overlapping to allow some movement to form a flexible skeleton. The second structure consists of microscopic sized spicules, which grow in the body wall to strengthen it. The plates or ossicles range in size from microscopic to about 33 mm, and may be reach 150 mm in length. They are made of calcite with a high content of magnesium (4% -16% Mg2+), and look under polarized microscope as a single crystal. This facilitates the process of identifying the remains of Echinoderms in thin section or hand samples.

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Fig. XII.3. Parts of the water vascular system in Echinodermata (http://en.wikipedia.org/wiki/Echinoderm).

Pentameral symmetry Most echinoderms have radial pentameral symmetry. The radial part of the test is the ambulacrum as in sea stars or sea lilies or fragile stars. It may be superimposed on the test as in sea urchins. Very few animals have bilateral symmetry, so it is easy to identify echinoderms. From 1-2% of individuals may deviate from the pentameral symmetry to become forms with tertiary, tetra and hexameral symmetry. Appendages Echinoderms usually have appendages, made up of small plates. These appendages may be small or large in size. The function of appendages may be protection (such as pedicellariae and spines) or gathering food (such as arms in the sea stars) and in fixation (such as lily stems and hold fast). Classification The phylum Echinodermata is subdivided into five subphylum and 20 classes depending mainly on the morphology of the skeleton in the mature stage. 1. Subphylum Crinozoa Echinoderms with spherical cups, and rigid connecting plates. Most Crinozoa have long protruding arms (Fig. XII.4), an open water vascular system and tube feet. They are mostly covered with calcite plates, showing pentameral symmetry. The mouth is in the center of the upper surface, and the anus is in the lateral side. Most of them do not have hydropores, gonopores and secondary respiratory components. They are mostly fixed on the substratum, both with long stems by cirri or rootlets (Figs. XII.4 and XII.5) or directly by the theca. From the Middle Cambrian to Recent, there are about 1025 genera in two classes.


Fig. XII.4. Morphology of a crinoid (http://en.wikipedia.org/wiki/Echinoderm).

Fig. XII. 5: Morphology of a crinoid stem (http://en.wikipedia.org/wiki/Echinoderm).

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2. Subphylum Blastozoa Echinoderms with a spherical theca. The theca consists of tighting connected plates. The animal has brachiols for gathering food and is fixed on special parts of tube feet. Plates are arranged in pentameral symmetry. The mouth is in the center of the upper surface, and the anus is in the lateral side. Most of them have hydropores, gonopores and secondary respiratory components. They are mostly fixed on the substratum by stems. From early Cambrian to Permian (extinct subphylum), there are about 233 genera in five classes. 3. Subphylum Asterozoa Star shaped echinoderms with a five-arm disk (Fig. XII.6) that consists of tight plates. Each arm has an ambulacral groove. Coelomic theca extends in arms, and some arms consist of articulated plates like vertebras and are different from the central desk (brittle star). Ambulacral grooves on arms include the open water vascular system, and on them pore pairs are present. Skeletal plates are numerous and small in size. The pentameral symmetry is clear. The mouth is in the center of the lower surface, and the anus (if present) is on the upper surface. The madreporite is in several positions. Most of them have secondary respiratory components. From the early Ordovician to Recent, there are about 755 genera in two classes.

Fig. XII.6. Morphology of a star shape Asterozoa.

4. Subphylum Homalozoa Echinoderms with a flattened test, asymmetry to bilateral symmetry. Theca with well connected plates and plates that are able to expand may have one or more appendages like brachial (cover have tube feet pores). The mouth is on the lower surface, and the anus is in the lateral side or in the other side of the theca. Some have lateral secondary pores (hydropores, gonopores) and in other secondary respiratory components. From the middle Cambrian to the middle Devonian (extinct subphylum), there are about 49 genera in four classes. 5. Subphylum Echinozoa Echinoderms with globular, flattened, cylindrical and fusiform tests. Their skeletons range from tightly sutured to reduced and with sclerites, with a closed water vascular system and tube feet exposed through pores of ambulacral areas. They mostly have no feeding appendages such arms, brachils or stems for fixation. The skeleton is mostly with several plates, arranged in good pentameral symmetry. They mostly have a mouth and an anus on the two sides of the skeleton, and also have gonopore or maderporite. One of the gonopores is close to mouth. From the early Cambrian to Recent, there are about 1018 genera in seven classes. In this book, the concentration will be on class echinoidea.


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Class Echinoidea The class Echinidea is the largest class of subphylum Echinozoa and the most important in the stratigraphy of post-Paleozoic rocks. Internal anatomy The gut (the most important parts of the interior organs) extends from the mouth to the anus, which is located on the upper surface from the posterior side, twisted in the form of a helical (spire). The circumoral ring is surrounded by the gut and is directly above the Aristotle lamp or above the peristome. The stone canal connects the ring canal with a madreporite. The five radial canals of the ambulacral areas end in the upper surface by ocular pores. The five radial canals of the interambulacral areas end in the upper surface by gonopores. Morphology of the skeleton Sea urchins have spherical or compressed skeletons (Figs. XII.7 and XII.8) consisting of several plates which are arranged in a radial manner, and they are in two types of paired rows. The first type is called ambulacral areas in which each plate has a hole or a pair of holes, from which tube feet are extended. The other type alternates with the first one and is called the interambulaclar areas. The free-moving spines are attached by the skeleton through tubercles on the outer regions of the plates. Most echinoids have pedicellariae, which are carried on small stems. The function of pedicellariae is defense and nutrition, but because of their fragile nature they are lost in the case of fossils. The mouth and its surrounding tissues is called the peristome. It occurs on the underside of the test. The peristomial notches are slit-like openings may exist on the edge around the mouth, and from them pressure compensating organs extend out from the water vascular system.

Fig. XII.7. Morphology of aboral surface of an echinoid (http://en.wikipedia.org/wiki/Echinoderm).

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Fig. XII.8. The periproct and peristome in regular echinoid (http://en.wikipedia.org/wiki/Echinoderm).

In many echinoids, the anus and surrounding tissues are called a periproct. It is locateed on the upper surface and is surrounded by a ring of plates called the apical system. The apical ring consists of 10 plates, five of which are called genital plates, which are located above the interambulacral regions which is perforated by tubes that come out outputs of reproduction. One of the genital plates acts as madriporite with its several pores leading to the water vascular system. The other five plates to be called ocular plates, which is located above rows of ambulacral areas. Classification of Echinoids The commonly used classification of the echinoidea is the two orders: Regularia and Irregularia. In regualrian sea urchins, the periproct exists inside the apical system and is described in this case as central, and its edges are circular (Fig. XII.8). Regularian echinoids may include ambulacral areas with simple (primaries) or compound plates (consisting of more than one plate) and covered with large tubercles. Ambulacral areas in regularia may extend from the apical system on the upper surface to the peristome on the lower surface of the test, they are described in this case as simple. In irregualrian sea urchins, the periproct leaves the apical system backwards, has bilateral symmetry and is usually elongated from the front to back. The periproct is described as supermarginal when it leaves the apical system backward and still on the upper surface. It is described as marginal when it exists on the margin, and is described as submarginal when it reaches the lower surface of the test. In all cases the periproct moves on the interambulacral area. Ambulacral areas in Irregularia may end on the upper surface of the test, and they are described in this case as petaloid. In heart-shaped sea urchins, the petaloids may be present in depressed areas The function of tube feet in the anterior ambulacral area is sensory or keeping the connection of the burrow in which the animal lives with the surface water. The function of tube feet in the posterior ambulacral areas is respiration. Many of the Regularia and Irregularia have elongated paired of ambulacral pores called phylloides on their lower surface close to the peristome. Tube feet that extend from these phylloides are used in feeding and fixing the animal to the sea floor. The plates of ambulacral areas only in all sea urchins except in sand dollars of the Clypeasteroids, containing one pore or a pore pair. In sand dollars from the Clypeasteroids they have in addition to these pore pairs more numerous and smaller pores called accessory pore in all ambulacral and interambulacral regions. From these pores extend tube feet used in the attachment to sand grains or in the transfer food.


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Some sand dollars have a hole or lunule near the edge of their tests. This is where sand and nutrients pass through the lunule to food grooves on the oral surface that transport the material to the mouth. Modes of Life Sea urchins provide the finest examples of the adaptation of animal morphology to different ways of life. It can be summarized in the following three types: 1. 2.

3.

Free active epifaunal: These echinoids live above the hard bottom and are represented by Regularia with their strong and large spines, with the presence of a periproct on the upper surface and a peristome in the lower surface and in the large size and centered of the mouth. Burrowing: These are represented by most Irregularia, particularly the Spatangoids with their small, weak and numerous spines. Moreover, they have a different distribution and shape of tube feet and leave the periproct backward (to be far from food entering the burrow) and leave the peristome arterially (to be far from the periproct which moves backward) and small size of the mouth (to become suitable for minutesized food). Semi-buried (Sand Dollars): These are adapted by their compressed, disk-shaped tests and the presence of open cabins.


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Questions on Phylum Echinodermata 1st Question: Choose the correct answer 1. 2. 3.

Echinoderm organisms have: a) exoskeletons b) endoskeletons

c) some without skeletons

The skeleton in Echinodermata is called: a) test b) shell

c) carapace

The skeletal mineral in Echinodermata is: a) Aragonite b) Calcite

c) Mg-Calcite

4.

The Echinoid skeleton consists of: a) one piece b) numerous units

5.

Each skeletal element of echinoid test consists of: a) monocrystal b) numerous crystals

6.

Skeletons of Echinoderms have the design: a) Sclerites b) Theca

c) both are present

Examples of theca design: a) Ecinoid tests

b) Crinoid crowns

c) In Holothuroids

Echinodermata are: a) all marine

b) some inhabit fresh water

c) In both a & b

7. 8. 9.

The mode of life in echinodermata is: a) Benthonic b) Nekton

c) Plankton

10. All species in phylum Echinodermata are living: a) Epifaunal b) Infaunal

c) a or b are possible

11. Echioderm species are: a) Vagile excepte crinoids

c) Vagile

b) Sessile

12. The apparent symmetry in all echinoderms are: a) Pentameral b) Radial

c) Bilateral

13. The water vascular system is characteristic for: a) only Echinodermata b) it could be present in other phyla 14. The apical system consists of: a) Ten identical plates b) Five ocular & five genital plates 15. Anus is located: a) always inside the apical system

b) inside & outside the apical system

16. When all plates of the apical system surrounds the anus, it is termed as: a) Monocyclic b) Dicyclic

d) In a & b


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17. The presence of many irregular echinoid in life position in one bed indicates that: a) depositional environment with soft substrate, low energy b) depositional environment with hard substrate, high energy c) no relation 18. Regular echinoids inhabit environments with: a) hard substrates as rocky bottoms & reefs b) soft bottom as sandy & muddy floor c) both conditions 2nd Question: Complete 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

The water vascular system consists of the following parts: ……………… The functions of the water vascular system ……………… The bases of classification of Class Echinoidea are ……………… The function(s) of tube feet in echinoides ……………… The function(s) of spines in Regular Echinoides ……………… The function(s) of spines in Irregular Echinoides ……………… The Echioid test consists of ……………………………………………… The ……………… system (also called Ocular ……………… ring). The ………………, which surrounds the anus in regular echinoid. The ………………, which surrounds the mouth and present always in the lower surface (the oral surface).

3rd Question: Justify 1.

Presence of water vascular system in echinoderms.

4th Question: Label

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CHAPTER XIII

PHYLUM GRAPTOLITHINA

Objectives 1. 2. 3. 4. 5. 6.

Define rhabdosome, sicula and stipe. State the composition of the wall and embryonic theca. Compare between planktonic and benthonic Graptolithina. Describe the morphology of the Graptolithina skeletons. Compare between the Order Graptolitoidea and the Order Dendroidea. State the geologic range of the Order Dendroidea. Overview

Graptolithina represent an extinct class of the phylum Hemichordata. They are entirely marine planktonic and benthonic. The planktonic group was highly diverse and more frequent than benthic ones. The Graptolithina lived in branched and complicated colonies; some form simple straight chains (3-5 mm to more than one meter in length, 5-10 cm in width and 10-15 cm in height). They are preserved in black shale as compressed carbonized impressions, and are sometimes replaced by pyrite and some are well preserved in limestones and flint. Colonies were composed of short tubes and connected by a common canal. Skeletons of protein. From the Cambrian to Pennsylvanian (extinct class), it includes 240 genera and 1800 species. Morphology Most Graptolithina secreted a skeleton (rhabdosome), arising from an embryonic conical individual of minute size called a sicula. It is believed that the sicula is the first individual of the colony, which is formed by sexual reproduction. On the embryonic theca, there are chains of successive tubes called branches or stripes, which arise from the sicula by budding. Some colonies (rhabdosomes) consist of one branch, others consist of two or more branches or more. The embryonic theca consists of a primary theca (prosicula) in the shape of a tapered cone (Fig. XIII.1). It extends into changed (metamorphic) theca. The first theca (first sicula) arise from the base of the metamorphic theca. From the cone of primary theca a nema arises (virgula if present within the colony or within its wall). There are two main types of individual theca in the rest of the colony: Large sized theca, called autotheca, and small sized theca called bitheca. Each theca has rounded or constricted aperture. Some apertures have spines and anchors.

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Fig. XIII.1. Sicula and first theca of a planktonic graptolite rhabdosome showing major characters of sicula and first theca (Berry, 1987).

Graptolithina colonies (Figs. XIII.2 and XIII.3) composed of four or fewer stipes commonly are oriented such that the sicula apex pointed upwards. Using that orientation, the rhabdosome is termed pendent if the stipes are directed downward and the thecal apertures essentially face each other. Those rhabdosomes in which the stipes are developed normal to the sicula are termed horizontal. The rhabdosomes are termed reclined if the stipes are directed upward but do not touch. The rhabdosome is termed scandent (uniserial or biserial) if the stipes are directed upward and the virgula is enclosed. The wall of the skeleton consists of two layers: External cortical tissue and the internal fusellar tissue. The cortical tissue in planktonic graptolithina is reduced compared with that of the sessile graptolithina. Classification Order Dendroidea Attached branching graptolites (Fig. XIII.4), characterized by two sizes of theca, the larger autotheca and smaller bitheca. Rhabdosomes are commonly with many branches. Branches in some graptolites are connected by rod-like structures formed from clusters of theca. Autotheca and bitheca are linked by a stolonal system. In most species, stolons include hard, black, organic substance, probably proteinaceous; stolons are housed in the periderm. From Cambrian to Pennsylvanian, there are 30 genera. Order Graptolitoidea Planktonic graptolites of one type theca equivalent to autotheca in other graptrolites, on few stipes (Fig. XIII.5). In some colonies, autotheca have progressively different shapes and sizes along the stipes. Stolonal system of soft tissue only peridermal tissues that include many fewer layers than in most dendroides. From the Ordovician to Early Devonian, there are 185 genera.

Phylum Graptolithina

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Fig. XIII.2. Three planktonic graptolite rhabdosomes showing major morphological features. (A) Didymograptus (pendent or tuning fork form). (B) Isograptus (a reclined rhabdosome). (C) horizontal form of Didymograptus (Berry, 1987).

Fig. XIII.3. Planktonic graptolite rhabdosome (a biserial scandent form) freed from its rock matrix (Berry, 1987).

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Fig. XIII.4. Fragment of the dendroid Dictyonema rhabdosome showing thickened basal part of rhabdosome and branching pattern (Berry, 1987).

Fig. XIII.5. Fragment of planktonic graptolites (http://en.wikipedia.org/wiki/Graptolithinia).

Phylum Graptolithina

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Questions on Class Graptolithina 1st Question: Choose the correct answer 1. 2.

Skeletons of class Graptolithina are of: a) Calcite b) Aragonite The geologic range of Graptolithina is: a) From Cambrian to Pennsylvanian

c) Protein b) Cambrian to Recent

2nd Question: Give the scientific term to the following definitions 1. 2. 3. 4. 5.

The first individual of the Graptolithina colony, which is formed by sexual reproduction. Rhabdosome with stipes directed downward and the thecal apertures essentially face each other. Rhabdosomes with stipes developed normal to the sicula. Rhabdosomes with stipes directed upward but do not touch. Rhabdosome with stipes directed upward and the virgule is enclosed.


The …………… is the first individual of the Graptolithina colony. Successive branch or stripe, arise from sicula by …………… Graptolithina colonies composed of stipes commonly oriented such that the sicula apex pointed …………… Rhabdosome is termed …………… if the stipes are directed downward and the thecal apertures essentially face each other. Rhabdosomes in which the stipes are developed normal to the sicula are termed …………… Rhabdosomes are termed …………… if the stipes are directed upward but do not touch. Rhabdosome is termed …………… if the stipes are directed upward and the virgule is enclosed.

5th Question: Label

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CHAPTER XIV

TRACE FOSSILS (ICHNOLOGY)

Objectives 1. 2. 3. 4. 5. 6.

State examples of trace fossils. List the importance of trace fossils. Define trace fossils and ichnology. List the forms of feeding burrows. Explain the behavioral classification of trace fossils. Differentiate between taxonomic and depositional classification of trace fossils. Overview

Trace fossils are preserved structures in sedimentary rocks that express the vital activity of organisms (movement, nutrition, permanent or temporary habitat …) without the body fossil or parts (remains) of it. Trace fossils have applications in the fields of stratigraphy, sedimentology and paleoecology. It is also a type of primary sedimentary structure and called bioturbation. Bioturbation is represented by burrows and the effects of movement on soft sediments (tracks), trails, borings, coprolites and fecal pellets. Importance of Trace Fossils 1. 2. 3. 4. 5. 6.

They may occur in sedimentary rocks lacking body fossils such as sandstones (Seilacher, 1967). By their trace fossils, these rocks can be stratigraphically correlated and classified. Some trace fossils can be used as local index fossils to date the rocks in which they are found, such as the burrow Arenicolites franconicus which occurs only in a 4-cm layer in the Triassic Muschelkalk epoch, throughout wide areas in southern Germany (Schlirf, 2006). The base of the Cambrian period is defined by the first appearance of the trace fossil Treptichnus pedum (Gehling et al., 2001). Diagenesis can destroy or distort body fossils but has little effect on trace fossils and may even enhance their preservation. They are preserved in the same locality within sediments. Traces resulting from biological activity are mostly larger in size than the organisms that produce them. Classification There are three types of the classification of trace fossils as follows.

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1. Taxonomic classification Classification is based on binomial nomenclature (genus and species names) and follows the zoological code, even if the traces are produced by plants. The trace takes a name that is not related to the organism that did it. It is often difficult to match the trace to the organism that produce it due to the following reasons:   

It may be impossible or difficult to find the trace and the body fossil together. Several organisms can produce similar traces. One organism may produce different traces according to its life periods, different activities, environments, seasons and sediments.

According to the above mentioned reasons, the taxonomic classification of trace fossils is not important in applied fields of invertebrate paleontology. 2. Depositional classification Description of a trace fossil is according to the position within the bed, on the upper bed surface or the lower bed surface (Fig. XIV.1). The importance of this is to determine whether the trace fossil was formed after or before the deposition of a certain bed, especially on unconformity surfaces, which is important for determining the depositional history. A trace fossil is called full Relief when it is completely find within a bed. When the trace fossil is present on the bed surface, it is called Semirelief, which is divided into: Epirelief if it occurs on the upper surface of the bed, and Hyporelief if it occurs on the lower surface of the bed.

Fig. XIV.1. Classification of trace fossils according their position from beds surfaces (modified after Dodd and Santon, 1990).

Trace Fossils (Ichnology)

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3. Behavioral classification Since several organisms may produce similar traces and one organism may cause different traces according to its life activities, environments, seasons and sediments, certain environmental conditions cause certain behavior activities. The categories reflect the general case (purpose) of the trace, resulting from the organism behavior. Traces on behavior bases are classified into several divisions: (a) Dwelling traces (Domichnia) Burrows and borings of vertical, unbranched, cylindrical or U-shaped, providing more or less permanent homes for animal. (b) Feeding traces (Fodinichnia) Burrows of sediment feeders, usually with a distinct three-dimensional aspect. (c) Traces of locomotion (Repichnia) Evidence of locomotion either on or through the substrate, usually straight or generally curved in shape, made by organisms traveling from one place to another. (d) Resting or hiding traces (Cubichnia) Fillings of shallow excavations that usually mirror the morphology of the trace marker (Boardman et al., 1987). (e) Grazing traces (Pascichnia) Grooves, furrows and other structures produced by mobile sediment feeders that are primary twodimensional in aspect. Common Ichnogenera Cruziana (Fig. XIV.2) Excavation traces marks made on the sea floor which have a two-lobed structure with a central groove. The lobes are covered with scratch marks made by the legs of the excavating organism, usually a trilobite or allied arthropod. Cruziana are most common in marine sediments formed during the Paleozoic era, particularly in rocks from the Cambrian and Ordovician periods. Over 30 ichnospecies of Cruziana have been identified.

Fig. XIV.2. Cruziana from the Devonian Brallier Formation or Harrell Formation (http://en.wikipedia.org/wiki/Cruziana).

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Skolithos (Fig. XIV.3) One of the well-known occurrences of Cambrian trace fossils from this period is the famous “Pipe Rock” of northwest Scotland. The “pipes” that give the rock its name are closely packed straight tubes, which were presumably made by some kind of worm-like organism. The name given to this type of tube or burrow is Skolithos, which may be 30 cm (12") in length and between 2 to 4 cm (0.8 to 1.6") in diameter. Such traces are known worldwide from sands and sandstones deposited in shallow water environments, from the Cambrian period (542–488 Ma) onwards.

Fig. XIV.3. Skolithos trace fossil (http://en.wikipedia.org/wiki/Trace_fossil).

Thalassinoides (Fig. XIV.4) Burrows occur parallel to the bedding plane of the rock and are extremely abundant in rocks, worldwide, from the Jurassic period onwards. They are repeatedly branched with a slight swelling present at the junctions of the tubes. The burrows are cylindrical and vary from 2 to 5 cm (0.8" to 2") in diameter. Thalassinoides sometimes contain scratch marks, droppings or the bodily remains of the crustaceans that made them.

Fig. XIV.4. Thalassinoides burrows produced by crustaceans from the Middle Jurassic, Makhtesh Qatan, southern Israel (http://en.wikipedia.org/wiki/Thalassinoides).

Trace Fossils (Ichnology)

135

Questions on Trace Fossils 1st Question: Choose the correct answer 1.

Classification of trace fossils based on binomial nomenclature is: a) taxonomic classification b) depositional classification

2.

Classification of trace fossils according to position of trace fossils is: a) taxonomic classification b) depositional classification

3.

Trace fossil that is completely found within the bed is: a) semirelief b) full relief

4.

Trace fossil present on bed surface is: a) semirelief b) full relief

5.

Trace fossil that occurs on the upper surface of the bed is: a) Hyporelief b) Epirelief

6.

Trace fossil that occurs on the lower surface of the bed is: a) Hyporelief b) Epirelief

c) full relief

7.

Burrows and borings of vertical, unbranched, cylindrical or u-shaped are: a) dwelling traces b) feeding traces c) resting traces

8.

Burrows of sediment feeders, usually with a distinct three-dimensional aspect are: a) dwelling traces b) feeding traces c) resting traces

9.

Filling of shallow excavations that usually mirror the morphology of the trace marker are: a) dwelling traces b) feeding traces c) resting traces

10. Burrows of sediment feeders that are primary two-dimensional in aspect are: a) grazing burrows b) feeding traces c) resting traces 2nd Question: Give the scientific term to the following definitions 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Preserved structures in sedimentary rocks expressed the vital activity of organisms. Classification of trace fossils based on binomial nomenclature (genus and species names). Classification of trace fossils according to position of trace fossils. Trace fossil is completely found within the bed. Trace fossil presents on bed surface. Trace fossil occurs on the upper surface of the bed. Trace fossil occurs on the lower surface of the bed. Burrows and borings of vertical, unbranched, cylindrical or u-shaped. Burrows of sediment feeders, usually with a distinct three-dimensional aspect. Filling of shallow excavations that usually mirror the morphology of the trace marker. Burrows of sediment feeders that are primary two-dimensional in aspect.


136 3rd Question: Complete 1. 2. 3. 4. 5.

There are three types of classification of trace fossils: ……………, …………… and …………… Trace fossil is called …………… when it is completely found within the bed. Trace fossil is called …………… when it is present on bed surface Trace fossil is called …………… when it occurs on the upper surface of the bed. Trace fossil is called …………… when it occurs on the lower surface of the bed.

4th Question: Justify 1. 2. 3.

It is difficult to match between the trace and the body fossil did it. The taxonomic classification of trace fossils is not important in applied fields of invertebrate paleontology. The depositional classification of trace fossils is important.

5th Question: Write down on 1. 2. 3.

Importance of trace fossils. Behavioral classification of trace fossils. Depositional classification of trace fossils.

REFERENCES

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APPENDIX OF SCIENTIFIC TERMS

Agoniatitic suture: A suture line that consists of a few simple undivided lobes and saddles. Ammonitic suture: A suture line that is characterized by serrated lobes and saddles. Amphidetic: A type of pelecypod ligament located above the hinge line and in anterior and posterior sides. Ancestrula: The first individual formed through sexual reproduction in bryozoans colonies. Anisomyrian: A pelecypod shell that has two unequal adductor muscle scars. Asconoid sponges: The simplest structure of sponges, in the form of simple tube, perforated by pores. Atolls: Circular or horse-shoe coral reefs, situated on submerged islands. Autozooids: The feeding individuals of bryozoans. Barrier Reefs: Coral reefs separated from the continent by a lagoon. Brachidium: A long bar-like loop (tie shoe) support the lophophore in brachiopoda. Carbonization: Change of the original plant or animal material to a thin film of carbon. Ceratitic suture: A suture line characterized by rounded and undivided saddles, and serrated lobes. Cerioid: A coral form in which the wall between each two adjacent hexa-corallities becomes one wall. Choanocytes: The inner layer of sponge that consists of variously spaced flagellate-collared cells. Delthyrium area: A triangular area located between the pedicle foramen and the umbo of the brachial valve of brachiopoda. Dendroid: A coral form in which individuals lined up and held together to form branching forms. Desmodont: A type of pelecypod dentition in which teeth reduced or absent, replaced by some ridges on the hinge line. Dimyrian: A pelecypod shell with two adductor muscle scars. Dysodont: A type of pelecypod dentition having small teeth, close to the valve edge. Encrusting Zoaria: A bryozoan colony consists of a single or several layers of individuals, attaches on hard substrates. Epirelief: A trace fossil that is present on the upper surface of a bed.

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Appendix of Scientific Terms

Erect flexible Zoaria: A bryozoan colony like a tree, fixed with substratum only from the base. The joint material which links between branches is an organic material. Erect rigid Zoaria: A bryozoan colony like a tree, fixed with substratum only from the base. Branches connect mostly with calcified materials. Fossil diagenesis: Changes that take place to the skeleton after burial in sediments. Fossil record: Number of fossils that are known through publications in the literature, magazines and scientific journals. Fossilization: Transfer of the organism from the biosphere to the lithosphere. Fossils: Remains or traces of living organisms. Fringing reef: Coral reefs form along the coasts, connects with continents or volcanic islands. Full relief: A trace fossil that is completely found within a bed. Goniatitis suture: A suture line consists of numerous undivided lobes and saddles; typically eight lobes around the conch. Heterodont: A type of pelecypod dentition having cardinal teeth and lateral teeth either in front and/or behind the beak. Hinge: A broad area that carries teeth separated by sockets under the umbo of a pelecypod shell. Homeomorphy: Phenomenon means that shells may be similar in their external features, while different in their internal structures and morphological features. Homonyms: Two species different in morphology and have the same name. Hydnopheroid: Corals with centers arranged around hills. Hyporelief: A trace fossil that is present on the lower surface of a bed. Graptolithina: An extinct class of the phylum Hemichordata. Index Fossils: Fossils characterized by short stratigraphic range, wide geographical range and used in determination of relative time of the sediments bearing them. Integripalliate: A pelecypod shell with complete pallial line. Irregularia: A group of echinoids in which periproct leaves the apical system backwards and with petaloid or subpetaloid ambulacral areas. Isodont: A type of pelecypod dentition having very large teeth, symmetrical around the resulium. Isomyrian: A pelecypod shell has two equal adductor muscle scars. Kingdom: The largest taxonomical unit and includes a large number of phyla. Leuconoid sponges: The largest and the most complex sponges.


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Lophophore: A fleshy hollow hairs provider of cilia and occupies the bulk of the mantle cavity of a brachiopod shell, used for pumping water into the shell, filter of food and breathing. Meandroid: A coral in which corallites fit together and the wall between them disappear, and looks like brainshape valleys. Mesenchyme: The middle gelatinous layer of sponge skeleton. Monomyrian: A pelecypod shell has only one adductor muscle scar. Opisthogyral: A pelecypod beak inclined towards the posterior side. Opithodetic: A type of pelecypod ligament located in an elongate pit behind the umbo and above the hinge line. Orthoceratitic suture: A suture line characterized by no lobes or saddles, except broad wind – if any – or round lobes and saddles. Orthogyral: A straight pelecypod beak not inclined to any side. Pachydont: A type of pelecypod dentition having very large, heavy and hard teeth. Paleontology: Study of life through geologic time. Pedicle: A soft part emits from the pedicle valve to fix some brachiopods on the substratum. Periproct: The anus and surrounding tissues in many echinoids. It is located on the upper surface and surrounded by a ring of plates called apical system. Peristome: The mouth and its surrounding tissues of echinoids. It is located on the underside of the test. Permineralization: Deposition of mineral material from underground solutions in pore spaces of buried remains. Phaceloid: Coral form in which individuals take parallel or semi-parallel tubes coherent with calcareous deposits. Pinacocytes: The outer layer of sponge, consists of closely spaced leathery cells. Placoid: Corals with separated corallites, each corallite has its own wall, and engage with each other by thin desipments between walls. Prosogyral: A pelecypod beak inclined towards the anterior side. Recrystalization: Conversion of less stable compounds into a more stable form. Regularia: A group of echinoids characterizes by central periproct, central peristome and simple ambulacral areas. Replacement: Complete replacement of skeletal tissues by new mineral material. Resilum: A type of pelecypod ligament located as triangular pit with isodont teeth. Schisodont: A type of pelecypod dentition having prominent bifurcating or diverging teeth.

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Semirelief: A trace fossil presents on the bed surface. Septa: Calcareous walls with a concavity toward the aperture (adorally) subdivided the cephalopod shell. Sicula: An embryonic conical individual of minute size represents the first individual of the Graptolithina colony. Most Graptolithina rhabdosome arising from it. Sinopalliate: A pelecypod shell with a sinus in the posterior edge of the pallial line. Siphuncle: It is a unique organ in cephalopods, consists of soft and solid parts and passes through the septa in an opening called septal foramen. Species: The essential unit in organism taxonomy and is the only objective taxonomical unit. Suture line: A line results from meeting the septum with the shell wall. It can be easily detected in the internal molds. Syconoid sponges: Sponges tend to be larger and with thick, folded wall than asconoids. Synonyms: Same species have different names in different countries. Taphonomy: Changes that take place to the organism after death and burial in sediments. Taxodont: A type of pelecypod dentition having a series of small parallel to sub parallel teeth which are perpendicular to the hinge line. Thamnasteroid: Corals lack a specific walls, and septa are converging. Torsion: The visceral mass of the gastropod animal rotates 180° to one side during development. Trace fossils: Preserved structures in sedimentary rocks and express the vital activity of organisms. Umbulacral grooves: The outer parts of tubular water vascular system, with delicate and free moving tube feet which controls the movement of these tube-feet of echinoids.

SUBJECT INDEX

E

A Agoniatitic suture 68 Ambulacral areas 119, 120 Ammonitic suture 68, 70 Amoebocytes 15 Amphidetic ligament 79, 81 Ancestrula 101, 104 Anisomyrian muscle scars 80 Annelida 43 Appendages 50, 113, 116 Articulata 91, 96 Asconoid sponges 17 Atolls 38 Autozooids 101

Echinodermata 113, 114 Encrusting Zoaria 102, 104 Epirelief 132

F Flexible Zoaria 102, 106 Fossil record 5 Fossilization 1, 20 Fossils 1 Fringing reef Zoaria 107 Full Relief 132

G

B

Gastropoda 53 Goniatitic suture 68, 69 Graptolithina 125

Barrier Reefs 38 Body chamber 65 Brachidium 92 Brachiopoda 3, 91 Bryozoa 101

H Hemichordata 125 Heterochonous homomorphus 95 Heterodont 78 Hinge 77, 78, 94 Homeomorphy 67, 95 Homonyms 11 Hydnopheroid corals 35 Hyporelief 132

C Carbonization 4 Casts 5 Cephalon 43, 45, 50 Cephalopoda 63 Ceratitic suture 68, 69 Cerioid corals 35 Choanocytes 15, 16, 17 Cnidaria 25 Commissure line 92 Coral reefs 37 Corals 3, 37

I Inarticularia 91, 96 Index Fossils 6 Integripalliate 80 Interambulacral areas 119, 120 Irregularia 120 Irregularian echinoids 120 Isochronus homomorphus 95 Isodont dentition 78 Isomyrian muscle scars 79

D Delthyrium area 92, 93 Dendroid corals 35 Desmodont 78 Diagenesis 1 Dimyrian muscle scars 79 Dysodont 78 145

Subject Index

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J Jelly fish 31

K Kingdom 9

L Leuconoid sponges 18 Ligament 77 Lophophore 91, 103

Prosogyral beak 81, 82 Pygidium 43, 45, 50

R Radiolaria 3 Recrystalization 2, 4 Regularian echinoids 120 Replacement 2 Replacement 4 Resilum 79, 81 Rigid Zoaria 120 Rugosa 33

M Madreporite 115, 119 Mammoth 3 Meandroid corals 35 Medusa 26, 27 Molds 4 Monomyrian muscle scar 80 Mortality 2

N Nema 127 Nummulitic limestone 1

S Schisodont dentition 78 Scleractinia 33 Sedimentary rocks 1, 6 Semirelief 132 Septa 64, 67 Sicula 125, 127 Sinupalliate 80 Siphuncle 64, 70, 71 Species 10, 11 Spongine 3 Suture line 65, 67 Syconoid sponges 18 Synonyms 11

O Opisthogyral beak 81, 82 Opithodetic ligament 79, 81 Orthoceratitic suture 68 Orthogyral beak 81, 82

P Pachydont dentition 78 Paleontology 1 Pallial line 80 Pedicle 91, 93, 97 Pelecypoda 77 Periproct 119, 120 Peristome 65, 119, 120, 121 Perminiralization 4 Phaceloid corals 35 Phragmocone 65 Pinacocytes 15 Placoid corals 35 Polymorphism 101 Polyp 25, 27 Porifera 15

T Taxodont dentition 78 Thamnasteroid corals 35 Thorax 50 Torsion 53, 54 Trace fossil 5, 131 Trilobita 49 Trochophore 53, 55 Trunk 43, 45

U Umbo 92

V Veliger 53, 55 Virgula 127

W Water vascular system 115, 116