Marine Shells of Goa

Sangeeta M. Sonak

A Guide to Identification

Marine Shells of Goa

Sangeeta M. Sonak

Marine Shells of GoaA Guide to Identification

123

Sangeeta M. SonakCentre for Environment and NaturalResource Management (CENRM)

Panaji, GoaIndia

and

SRUJANCaranzalem, GoaIndia

ISBN 978-3-319-55097-8 ISBN 978-3-319-55099-2 (eBook)DOI 10.1007/978-3-319-55099-2

Library of Congress Control Number: 2017935549

© Springer International Publishing AG 2017This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or partof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations,recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmissionor information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilarmethodology now known or hereafter developed.The use of general descriptive names, registered names, trademarks, service marks, etc. in thispublication does not imply, even in the absence of a specific statement, that such names are exempt fromthe relevant protective laws and regulations and therefore free for general use.The publisher, the authors and the editors are safe to assume that the advice and information in thisbook are believed to be true and accurate at the date of publication. Neither the publisher nor theauthors or the editors give a warranty, express or implied, with respect to the material contained herein orfor any errors or omissions that may have been made. The publisher remains neutral with regard tojurisdictional claims in published maps and institutional affiliations.

Printed on acid-free paper

This Springer imprint is published by Springer NatureThe registered company is Springer International Publishing AGThe registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

The book is dedicated to my son, Eeshan, whoactually began writing of this book.

Preface

The urge to say something, share useful knowledge upon a subject, is matchedperhaps, by the urge to know something on a subject. It is basically these urges thathave served as impetus to write this book on Conchology, the study of shellsproduced by living creatures called molluscs.

Conchology is concerned with study of shells; and Malacology, with shells andcreatures within (molluscs). As compared to Conchology, Malacology necessarilyinvolves much greater scientific and technical literature. At times, these factorsrender such study insipid and unappetizing to many. Conchology, to a great extent,involves collection, classification and the appreciation of the structure and designsof shells. Therefore, at least to some extent, this is a recreational activity for thosewho seek intellectual indulgence in these wonderful objects of the sea. This book is,therefore, an attempt to present the shells of Goa to scientific researchers andamateur shell collectors alike, so that they find in these wonderful objects of the sea,something useful and interesting in their respective pursuits. The book seeks to tieknots between popular science and research, science and hobby, and science andart.

This book is intended not only as a field guide to shells of Goa, but also thepresentation is aimed to offer a delightful learning experience to an amateur shellcollector. With this objective, the photographs of the shells presented in this bookare, as far as possible, ‘in situ’ photographs of shells in the same condition asactually found on the beaches of Goa. Shell collection offers a very meaningful andinformative pursuit to all those who seek pleasure in collecting these beautifulcolourful objects during their leisure hours. From children to aged and fromamateurs to professionals, people from various strata of the society enjoy shellcollection. The thrill of finding the desired shell is sometimes compared to the thrillof a hunt. The book will serve those who desire to learn science without anyprevious knowledge of the subject, with a small parcel of shells that they collectfrom the seashores of Goa.

Quest to bring science out of the laboratories and research papers of the aca-demia into the lives of people has guided writing of this book. The main challengein presenting this book was to achieve a balance, so that the presentation is not too

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scientific and technical to make it unexciting to the amateur shell collector or bereftof scientific classification and references, to make it uninteresting to academics. Thefocus of the book is shells and not molluscs. The objective of this book is tointroduce shell heritage and inculcate and encourage curiosity and scientific interest,not just among conchologists, but also local and tourist beach goers.

The book is divided into five chapters. Chapter 1 is aimed at familiarizingreaders to shells and molluscs, organisms that produce shells. Simple, non-technicallanguage with glossary of some scientific terms will help readers in this effort. Goa,though quite famous for its sun, sand and sea, is also a shell collectors’ paradise.Chapter 2 introduces Goa and her shell habitats, with picturesque coastline andvibrant ecosystems, to the shell collectors. Identification of shell specimen is pre-sented in Chap. 3. As written earlier, the aim is to help an amateur shell collectorwith identification of the shell specimen.

Shells have inspired not only scientific research but also art and culture. Thecolours, the design and the ornamentation have served as source for art, culture andeven architecture. Chapter 4 on shell art and shell craft dwells upon the status ofshell art and shell craft in Goa. However, I wish to point out that I do not subscribeor encourage intense shell collection or killing, harming of any individual molluscfor its shell.

Chapter 5 deals with some interesting facts about shells such as importance ofshells and literary work related to shells and their writers. Lastly is an appendix thatgives a collection of some common quotes on shells. Finally, the book concludeswith a glossary explaining the technical terms used in the text.

A part of this book has received small amount of financial support fromDepartment of Science, Technology and Environment (DSTE), Government ofGoa. I wish to acknowledge Government of Goa and Mr. Levinsen Martins, andMr. S. Kotwale Directors, DSTE for the support.

I gratefully acknowledge contribution of Dr. Deepak Apte, Chief OperatingOfficer, Bombay Natural History Society, Mumbai, who validated my identificationof shell species.

I must express my gratitude to Kishore Lokre for the time he spent in readingchapters despite his busy schedule. Dr. Subodh Kerkar shared his work with me andoffered excellent photographs of his work that are presented in this book.

Rod LeGear, Vice President, Kent Archeological Society, shared their work onShell Grotto and also forwarded photographs of the Grotto for publication in thebook. I sincerely acknowledge Kent Archeological Society and Rod LeGear forthis.

Darryl Pereira, Managing Director, Reira Ventures, Saligao Goa, contributedlovely photographs of some beaches of Goa such as Colva, Agonda, Chapora,Vagator, Uttorda and Betalbatim. My friend, Dr. Prabha Devi from NationalInstitute of Oceanography (NIO), helped me in collection of sea shells. Mr. CarloEurico Santana da Silva shared information and photograph of his house with shellwindows, ‘Sat Buruza ghor’. Col. Leena Gurav introduced me to Assam RifflesMuseum and traditional dress of Naga tribes with cowries.

viii Preface

I must also express my gratitude to my colleagues at Centre for Environment andNatural Resource Management (CENRM) and SRUJAN for their immense supportto the project. Field assistance from Mr. J Kandolkar in collection of shells andlaboratory assistance from Bharati in cleaning of shells will be remembered. Manypeople have helped me in writing of this book. It is not possible to acknowledgeeach one by name here; however, their contribution is much appreciated.

As the book was going through its final stages of production, we were deeplypained at the untimely and sudden death of my brother-in-law, Satish Sonak, on 7thApril 2017. Satish was a constant source of encouragement and support. The bookhas one picture of a model of a Goan window with shells, presented to me by Satishand his wife Harshada. Thank you, Satish and Harshada.

It was my husband, Mahesh, who inspired me to write this book. From begin-ning to end, Mahesh’s support and motivation to this endeavour is immense. Mysister-in-law, Sushama Sonak, with her vast experience at National Book Trust,New Delhi, helped me with several interesting shell facts and also critically editedsome of the chapters. Writing of this book follows nostalgic memories of our son’s,Eeshan’s, childhood days. Mahesh and I enjoyed watching him collect shells onvarious beaches of Goa, during his childhood. Even today, he is fascinated by seashells, what he calls ‘wonders of the sea’. It is he who actually began writing of thisbook. I dedicate this book to Eeshan and to these lovely memories.

Panaji, India Sangeeta M. Sonak

Preface ix

Contents

1 Molluscs and Their Shells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Phylum Mollusca . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Various Marine Habitats of Molluscs . . . . . . . . . . . . . . . . . . . . . . . 41.4 Molluscan Shell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51.5 Classification of Molluscs Based on Shells. . . . . . . . . . . . . . . . . . . 6

1.5.1 Class Monoplacophora . . . . . . . . . . . . . . . . . . . . . . . . . . . 61.5.2 Class Polyplacophora . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.5.3 Class Aplacophora. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.5.4 Class Scaphopoda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71.5.5 Class Cephalopoda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.5.6 Class Gastropoda. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81.5.7 Class Bivalvia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.6 Extinct Classes of Molluscs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91.7 Shells of Class Gastropoda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

1.7.1 Structure and Description of a Gastropod Shell. . . . . . . . . 101.7.2 Classification of Gastropoda . . . . . . . . . . . . . . . . . . . . . . . 111.7.3 Shells of Class Bivalvia . . . . . . . . . . . . . . . . . . . . . . . . . . 151.7.4 Structure and Description of a Bivalve Shell . . . . . . . . . . . 151.7.5 Classification of Bivalvia. . . . . . . . . . . . . . . . . . . . . . . . . . 171.7.6 Further Subdivision of Veneridae . . . . . . . . . . . . . . . . . . . 20

1.8 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

2 Shell Habitats of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.1 Introduction to Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252.2 Ecology of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

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2.3 Coastline of Goa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332.3.1 Beaches of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

2.4 History of Shells of Goa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

3 Cataloguing of Shells. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 533.2 Classification of Shells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182

4 Shell Art and Shell Craft of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1854.1 Masterpieces of the World . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186

4.1.1 Shells as Signifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1864.1.2 Margate Shell Grotto . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190

4.2 Shells in Indian Sculpture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1934.3 Shell Art and Shell Craft of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . 194

4.3.1 Shell Windows of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . 1944.3.2 Kaavi Art of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1974.3.3 Shells in the Sand Art of Goa . . . . . . . . . . . . . . . . . . . . . . 1984.3.4 Shell Paintings of Goa. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2004.3.5 Shell Art at Museum of Goa . . . . . . . . . . . . . . . . . . . . . . . 2004.3.6 Shell Craft of Goa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2034.3.7 Shell festival of Goa or Tisreache fest. . . . . . . . . . . . . . . . 210

4.4 Uses of Shells by Humans Since Antiquities . . . . . . . . . . . . . . . . . 2104.5 Fossil Shells of Marine Molluscs Found in Himalayas . . . . . . . . . . 2114.6 Conservation of Molluscs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216

5 Some Interesting Known and Unknown Facts About Shells . . . . . . . 2195.1 Importance of Molluscan Shells . . . . . . . . . . . . . . . . . . . . . . . . . . . 220

5.1.1 To Living Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2205.1.2 Coastal Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2205.1.3 Climatic Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2215.1.4 Providing Links to Evolution . . . . . . . . . . . . . . . . . . . . . . 2215.1.5 Biostratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2225.1.6 Anthropological Studies . . . . . . . . . . . . . . . . . . . . . . . . . . 2225.1.7 Human Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2225.1.8 Rituals and Ceremonies . . . . . . . . . . . . . . . . . . . . . . . . . . . 2255.1.9 History and Mythology . . . . . . . . . . . . . . . . . . . . . . . . . . . 2265.1.10 Religion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2265.1.11 Ethnography Such as Place Names, Person Names

and Deities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2275.1.12 Human Culture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2275.1.13 Paintings, Murals and Other Forms of Art . . . . . . . . . . . . 229

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5.1.14 Early Warning System. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2295.1.15 Assassination Attempts . . . . . . . . . . . . . . . . . . . . . . . . . . . 230

5.2 Significance of Shell Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2305.3 Literary Work on Shells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231

5.3.1 Charles Lyell (1797–1875) . . . . . . . . . . . . . . . . . . . . . . . . 2315.3.2 Edward Forbes (1815–1854) . . . . . . . . . . . . . . . . . . . . . . . 2325.3.3 James Hornell (1865–1949). . . . . . . . . . . . . . . . . . . . . . . . 2335.3.4 Anne Morrow Lindbergh (1906–2001) . . . . . . . . . . . . . . . 2345.3.5 William McGuire Bryson (Born 1951) . . . . . . . . . . . . . . . 2355.3.6 Janine Benyus (Born 1958) . . . . . . . . . . . . . . . . . . . . . . . . 236

5.4 Shell-Related Idioms and Proverbs . . . . . . . . . . . . . . . . . . . . . . . . . 2365.5 Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237

Appendix: Some quotes related to shells . . . . . . . . . . . . . . . . . . . . . . . . . . 241

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249

Contents xiii

About the Author

Dr. Sangeeta M. Sonak is a marine biologist. Currently she is the Director of anon-governmental research organization, Centre for Environment and NaturalResource management, which aims at promoting activities relating to protection ofenvironment. She has several years of research experience of guiding research teamsand coordinating research projects from various highly reputed national and inter-national organizations. She has been awarded prestigious international fellowshipssuch as Fulbright Scholarship under Fulbright-Nehru Environmental LeadershipProgram (FNELP) at Virginia Tech Institute, U.S.A., United States-IndiaEducational Foundation (USIEF) alumni award, JSPS Fellowship for SeniorScientist by the Japanese Society for the Promotion of Science (JSPS), ErasmusMundus Fellowship for Visiting Faculty to teach and conduct research at threeEuropean Universities by the European Commission. She has been awarded ShaktiPrerana Puraskar by Vidnyan Parishad (Science Congress), India in March 2014 inrecognition of ongoing commitment and dedicated service to environmental sci-ences, for innovative research at the frontiers of environmental science and forexceptional potential to shape the future through intellectual and inspiredleadership. She has authored and edited several research publications such as books,journal issues, journal papers, book chapters, technical reports, newsletters,conference papers and has presented her works at national and international levels.

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Chapter 1Molluscs and Their Shells

Abstract A shell is the hard outer cover or the external skeleton of the mollusc thatsecretes it and protects it from adverse environment and predators. Molluscs aresoft-bodied multi-cellular animals which secrete a hard calcareous shell for theirprotection. Each shell pattern is very specific to the particular species that syn-thesizes it. Therefore, there are shells of different shapes, colours, sizes, sculpturesand ornamentation, which is typical of the molluscan species that produce them.The identification of shells is therefore, with reference to the molluscan species,which produce them. The type of shell each molluscan species produces helps indetermining presence of that particular species in the marine environment and thushelps build a database of molluscs of that region. This chapter provides briefinformation on phylum Mollusca, different classes of the phylum, structure anddescription of molluscan shells, and salient features of shells of different speciesthat are found in Goa. In sum, the chapter sets the background for identification ofshells of various species of molluscs that are found in Goa.

Keywords Mollusc � Cambrian � Shell � Gastropod � Bivalve

1.1 Introduction

Our planet, Earth, was formed about 4.6 billion years ago. The age of Earth isclassified into various time units, with reference to the major geological events thathave taken place in the history of Earth. In the ‘geological timescale’, the largestunit of time is called ‘aeon’, which is divided into eras. The eras are in turn dividedinto periods, epochs and ages. These attempts to determine and classify Earth’s ageand map it on a geological timescale were largely successful because of the fos-sils of sea shells contained in the Earth’s strata (layer of sedimentary rock or soil).The first two-thirds of Earth history is referred to as the Pre-Cambrian. During thisPre-Cambrian period, major changes took place in the Earth’s crust, resulting in acooler Earth surface. Atmosphere and oceans were formed and life originatedon Earth. Molluscs made appearance in the Cambrian period about 540 ma

© Springer International Publishing AG 2017S.M. Sonak, Marine Shells of Goa, DOI 10.1007/978-3-319-55099-2_1

1

(million years ago). Molluscs are soft-bodied multi-cellular animals that are pro-tected by a hard calcareous shell. Different species of mollusc form different typesof shells. Shell size, colour, pattern and ornamentation often help in identificationand classification of the molluscan species. This chapter sets background foridentification of shells of various species of molluscs that are found in Goa.

The branch of science that deals with the study of molluscs is called malacology.This includes taxonomy, evolution, ecology as well as applied studies of molluscanspecies. On the other hand, conchology is the study of shells. While malacologistsstudy molluscs as the whole animal, conchologists deal only with the shells ofmolluscs. Most conchologists are shell collectors themselves, though some con-chologists may not opt for private and personal shell collections and may rely oninstitutional or other private shell collections for their research. Similarly, not allshell collectors are conchologists. Some shell collectors may be concerned withonly aesthetic value of shells and not their scientific importance.

1.2 Phylum Mollusca

Phylum Mollusca (larger group of animals to which molluscs belong) is one of theeight phyla that animal kingdom is divided into. It is the second largest phylum inthe animal kingdom; second only to phylum Arthrodpoda. It comprises some of theoldest and the most diverse groups of animals. Fossil records of early molluscs dateback to Early Cambrian period (about 540 ma). Molluscs originated in the sea andthen spread in freshwaters. In the Cretaceous period (145.5–65.5 ma), they wereable to inhabit terrestrial environments. They are now found in a wide range ofhabitats, from deep sea to terrestrial environments to freshwaters. The total diversityof molluscs recorded from India is 5169 species (MoEF 2014), representing around7% of the total global molluscan diversity. Marine molluscan diversity of Indiaincludes 3,400 species; however, there is no well-defined and updated checklist onmarine molluscs of India (Kumar and Ravinesh 2016).

As described earlier, they are soft-bodied animals protected by an external shell(Fig. 1.1). The name of the phylum Mollusca is derived from the Latin word‘molluscus’ meaning soft, which refers to their soft bodies. Technically, Pojeta andRunnegar (1976) describe molluscs as free-living metazoans that utilize a dorsalcalcareous exoskeleton to provide structural support for a muscular foot (or itsspecialized derivative) and to provide an enclosed space outside the body (mantlecavity) that is used for feeding, respiration, and sometimes, locomotion. Mostgroups of molluscs such as monoplacophora, gastropoda, bivalvia and rostroconchsmade appearance in the Early Cambrian period. Cephalopods appeared in theMiddle Cambrian period, Polyplacophorans in the Late Cambrian and Scaphopodain the Odrovician period.

Main parts of the body of a mollusc are a foot, a head and a visceral masscovered by a mantle that synthesizes a shell. Oxford dictionary meaning of the word‘mantle’ is a loose cloak or covering and the origin or source of the word is Latin.

2 1 Molluscs and Their Shells

The mantle covers the visceral mass and a mantle cavity containing gills. Althoughmolluscs are coelomates, the coelom (main body cavity) tends to be small. The footis situated at the ventral margin, whereas the visceral mass is towards the dorsalside. A radula or a rasping organ present in the anterior part of the digestive tract isa characteristic of most molluscs. Most molluscs use sexual reproduction.Generally, male and female sexes are distinct with the exception of some species,which are hermaphrodite. While in aqueous environment fertilization is external, itis internal in terrestrial snails (Fig. 1.2). Most common features in modern molluscs

Fig. 1.1 A live mollusc on abeach

Fig. 1.2 Externalfertilization in terrestrialsnails

1.2 Phylum Mollusca 3

are mantle cavity for respiratory and excretory functions, the radula and thestructure of the nervous system. Molluscs exhibit a wide range of diversity withrespect to other features. The shell and the radula are primarily responsible for thesuccess of the molluscs. The shell provides protection from predators and adverseenvironment and the radula along with jaws helps in tearing and biting pieces oflarge nutrient material. Radula, a tongue-like plate in the buccal cavity of themolluscs, is a feature unique to Phylum Mollusca. Radula is covered with teeth,which are used to scrape food particles into the mouth. Radula have adapted interms of number, shape arrangement and growth of teeth for diverse feedingmethods, especially in the gastropods, where number and shape of radular teeth areimportant taxonomic characters.

1.3 Various Marine Habitats of Molluscs

Molluscs have adapted to a wide range of habitats. They are found in intertidalwaters, mudflats, sandy shores, rocky surfaces, mangroves, marshes, coral reef andin estuarine ecosystems. Colonies of Tridacna crocea are seen on rocks in intertidalzone in Fig. 1.3a, b. Trochus, moon shells, helmet shells, tritons, nassa and babylonshells are found in the intertidal waters. Sandy shores generally support burrowingbivalves, and corkscrew shells. Sandy shores with high silt content are dominatedby detritus feeders such as Cerithiidae, horn shells and sundials. Coarse sandyhabitats provide shelter to deep burrowing organisms such as olive shells, moonshells, button shells, etc. Fine sand is inhabited by mitre, augur and cone shells.Rocky surfaces shelter a wide range of molluscs that can attach to substrata such aslimpets (Patella), whelks, periwinkles, nerites, rock shells, dove shells, frog shells,cone shells, oysters and mussels. Cowries, Thais and some species of Conus hide inrock pools and crevices. Melon conches are found in brackish estuarine waters, mud

Fig. 1.3 a Colonies of Tridacna crocea seen on rocks in intertidal zone. b Magnified view ofcolonies of Tridacna crocea

4 1 Molluscs and Their Shells

or mangrove swamps. Coral reefs provide refuge to diverse group of molluscs.Mangroves shelter some bivalves, telescopium sp, ceriths and horn shells. Tibia andconch shells inhabit deep sea.

1.4 Molluscan Shell

A shell is the hard outer cover or external skeleton of the mollusc that protects itfrom adverse environments and predators. The shell is secreted by mantle or pal-lium. Some cells produce a protein layer called conchiolin (a protein hardened withcalcium carbonate), while other cells secrete a fluid into the mantle cavity betweenthis conchiolin layer and animal tissues. Calcium ions excreted from the blood mixwith this fluid forming calcium carbonate. Calcium carbonate crystallizes onto theinner surface of the conchiolin producing a shell. The shell mainly consists of chitinand conchiolin. In most cases, only the outermost layer is all conchiolin. Whilemost mollusc shells are composed mainly of aragonite, those gastropods that layeggs with a hard shell use calcite (sometimes with traces of aragonite) to constructthe eggshells. Aragonite provides materials necessary for molluscs and also keepsthe pH of the water close to its natural level, which helps to prevent the dissolutionof biogenic calcium carbonate.

The shell may consist of three layers: the outer layer (the periostracum) made oforganic matter, a middle layer made of columnar calcite and an inner layer con-sisting of laminated calcite, often nacreous. Nacre (commonly called as mother ofpearls) is found in some groups of gastropods and bivalves such as top snailsbelonging to Family Trochidae or pearl oysters belonging to Family Pteriidae. Likethe other calcareous layers of the shell, the nacre is created by the epithelialcells (formed by the germ layer ectoderm) of the mantle tissue.

The shell of bivalves is composed of two lateral valves hinged together dorsally.The calcareous part of the shell consists of several layers and is secreted by themantle surface. When the valves close, the muscular inner fold of the mantle fold ofone side, the adductor muscle, gets compressed against that of the other side. Theperiostracum protects the underlying calcareous layers from dissolution, which isnecessary in hard-substrate burrowing species. The hinge ligament that connects thetwo valves dorsally is composed of elastic protein covered with periostracum.

Growth of the shell is rhythmic and continuous. The shell growth occurs byaddition of new bands of conchiolin and calcium carbonate along the existing edgesof the shell. Most shells are coloured because of the different pigments secreted bythe mantle. Yellow, red, brown and orange are the most common colours of themolluscan shells. The shells also have different shape, colour, size, sculpture andornamentation that are typical of different molluscan species. Hence, the type ofshell produced by each molluscan species helps to classify the organism up to thespecies level.

1.3 Various Marine Habitats of Molluscs 5

1.5 Classification of Molluscs Based on Shells

The system of classifying animals and plants was initially introduced by Swedishbiologist Carl von Linné (also called as Carolus Linnaeus). This system of Linneanclassification, which uses a two-word name practice, is called as binomial nomen-clature. The first name is its genus and the second part is species. The other hierar-chical levels are families, order, classes and phyla. Each of these levels may havefurther subdivisions such as superfamilies and sub-families. Living molluscs ofPhylum Mollusca are divided into seven classes, viz. Monoplacophora,Polyplacophora, Aplacophora, Scaphopoda, Gastropoda, Bivalvia and Cephalopoda.

Of these, Gastropoda comprises the largest class with almost 80% of livingmolluscs belonging to this class. Bivalvia is the second largest class of PhylumMollusca. These two classes, Gastropoda and Bivalvia, have considerably evolvedover time in order that they can better adapt to changing environment on Earth.They have developed several different ways of surviving in different environmentsand under various adverse situations. This has allowed them enhanced ability toexploit their natural environments and hence improved capacity to flourish.

Following section describes classification of mollusca. This classification is alsosummarized in Fig. 1.4.

1.5.1 Class Monoplacophora

Monoplacophors (meaning ‘with one plate’) or gastroverms are basically bilaterallysymmetrical segmented limpets that have a single, conical shell with eight pairs ofserially repeated muscle scars. Monoplacophors are very small, ovate or round witha long foot. Though they were supposed to be extinct earlier, some living specieshave been discovered in the last century.

Polyplacophora

Scaphopoda

Cephalopoda

Bivalvia

A conical shell with eight pairs of serially repeated muscle scars

Shield like shell with eight separate overlapping plates

Tusk shell with a hollow tube like structure

Lack any shell or presence of an internal shell except in Nautilus

A single coiled shell with diverse pa erns and colours

Shell with two separate symmetrical valves joined by a ligament

Gastropoda

Phylum Mollusca

Monoplacophora

AplacophoraShell without any plates

Fig. 1.4 Classification ofmollusc based on shells

6 1 Molluscs and Their Shells

1.5.2 Class Polyplacophora

Polyplacophors or chitons have elongated, flattened, bilaterally symmetrical bodies.The foot is long. Polyplacophors (with many plates) or chitons have shield likeshells that are secreted as eight separate plates. These shells have a head valve and atail valve separated by six intermediate valves. Each of these valves may becomposed of four separate layers. The outermost layer is periostracum, the next istegmentum followed by articulamentum and the innermost layer hypostracum. Ofthese, articulamentum is the thickest and the hardest layer. The valves are heldtogether by muscles and a cuticular girdle that lies between the tegmentum and thearticulamentum. Class Monoplacophora and Class Polyplacophora inhabit bottomsof deep oceans.

1.5.3 Class Aplacophora

Aplacophora (without plates) or solenogasters are wormlike, mostly very smallmolluscs covered with calcareous spicules. They do not have shells, but smallcalcareous spicules in their mantle. There is no head or specialized excretory organ(nephridia). The foot and mantle cavity are reduced. They are exclusively marine,benthic animals that feed on other benthic animals such as coelenterates or organicdebris. They have been recorded from very deep sea waters. Sea cucumber is themost familiar example of this class. In the recent years, Class Aplacophora isdivided into Caudofoveata and Solenogastres (Sigwart and Sumner-Rooney 2016).

1.5.4 Class Scaphopoda

The scaphopods are a small group of molluscs. Their tall, bilaterally symmetricalbody is contained in a hollow tube-like structure, open on both sides, one end wideand the other end narrow and pointed (tusk shaped). Scaphopods or tusk shells havetubular shells, which originate as a small cap-like structure. The edges spread outand surround larva during its development. They fuse along the opposite sides toform a tube. After metamorphosis, the growth occurs through the addition of shellto the circular edge of the anterior opening. Scaphopod shell consists of an outercovering of the shell called periostracum and two to four layers of aragonite. Theyare inhabitants of soft bottoms.

1.5 Classification of Molluscs Based on Shells 7

1.5.5 Class Cephalopoda

The cephalopods are considered to be the most highly evolved class of molluscs.They have a highly evolved visual system and tentacles. Cephalopods includesquids, cuttlefish and octopus, which are neurologically most advanced amonginvertebrates. They are all marine organisms, inhabiting all oceans and at differentdepths, from shallow coastal waters to great depths in deep ocean waters. Some arepelagic and remain drifting in ocean waters. They are also fast swimmers and areactive predators. Their head and mouth are surrounded by muscular sucker bearingtentacles that capture prey. Earlier cephalopods had external shells with chambersthat were interconnected by a tube. Most modern-day cephalopods have lostexternal shell and either lack any shell (for example, squids and octopus) or have aninternal shell. Only a few surviving species of Nautilus still have external shell.

1.5.6 Class Gastropoda

Gastropods or snails comprise the largest class of Phylum Mollusca. Characteristicfeature of this class is a single coiled shell. During larval development, gastropodsundergo a process known as torsion, wherein visceral mass of the animal twists androtates 180° to one side such that the posterior mantle cavity is situated over thehead. This rotation also results in helical coiling of the shell and asymmetricalstructure. The word Gastropoda comes from Latin word ‘Gasteropoda’, which isoriginated from two Greek words, ‘gaster’ meaning stomach and ‘podos’ meaningfoot. The torsion brings their foot in line with their digestive system. Hence thename. Gastropods have lungs unlike other molluscs and can easily inhabit diverseterrestrial environments. Gastropods exhibit diverse array of shell patterns andcolours, which may be results of adaptation to their natural habitat. Similarities ingastropod shells, therefore, depend more on the natural environments than evolu-tionary lineages. Most diverse, beautiful, colourful and attractive shells are pro-duced by Class Gastropoda.

1.5.7 Class Bivalvia

Bivalvia is the second largest class of molluscs. Bivalves have a bilaterally sym-metrical body that is laterally compressed and enclosed in a shell consisting of twovalves. The two valves of a bivalve are connected by an elastic ligament. They lackradula and head is considerably reduced. Most bivalves are filter feeders. The twovalves are typically mirror images of each other. Bivalve larva produces a singlecap-like shell called a pellicle. During larval growth, it is enclosed by two mantlelobes. Each of these lobes individually develops a separate centre of calcification,

8 1 Molluscs and Their Shells

producing two separate valves after larval metamorphosis. Bivalve shell, thus,usually consists of two valves. The shell, generally, has three layers: an outercovering of periostracum, a middle calcified shell layer and an inner nacre. Themiddle calcified layer of different species exhibits different patterns and helps in theidentification of species.

1.6 Extinct Classes of Molluscs

Molluscs have a remarkable fossil record, dating back to Early Cambrian period,due to presence of their shells. From the fossil records, it is evident that severalgroups of molluscs such as bellerophontids (Cambrian to Triassic; 540–201 ma)and rostroconchs (Cambrian to Permian; 540–251 ma) have become extinct.

Bellerophontoidea (renamed from the original Bellerophontacea) is a super-family consisting of extinct planospirally coiled globose molluscs, though this hasundergone a number of revisions since its establishment. Kaim and Nützel (2011)confirm eight Early Triassic species of Bellerophontoidea representing three genera(Dicellonema, Retispira, and Warthia) from two families (Bellerophontidae andEuphemitidae). Bellerophontoideans were globally distributed in the Griesbachian,Dienerian and Smithian (Early-to-mid-Early Triassic) and at some localities theyformed mass accumulations. One of the excellent Permian gastropod faunas wasdiscovered in the H.S. Lee Mine, near Kampar, Perak during exhaustive field workconducted by the Geological Survey of Malaysia. This fauna contained importantnew species which helped to enlarge our understanding of Upper Paleozoic gas-tropod phylogeny (Lyman 1972).

The Rostroconchia is a class of extinct Molluscs dating from the EarlyCambrian to the Late Permian. They have a single bilaterally symmetrical shell intheir larval stage, which transforms into two valves giving rostroconch adult anon-hinged, pseudo-bivalved shell enclosing the mantle and muscular foot. An adultrostroconch, therefore, lacks a functional hinge thus differing from bivalves. TrueRostroconchs appeared during the Ordovician, heavily competing with the bivalvesuntil their decline in the end-early Ordovician turnover. Rostroconchs are believed toshare common ancestry with the Bivalvia (Pojeta and Runnegar 1976; Waller 1998).

As the book presents the shells of Goa, only the shells of species recorded in Goaare described in the book. The shells of Gastropoda and Bivalva were found inabundance on various beaches of Goa. Molluscan species found in Goa, predomi-nantly belonging to the classes Gastropoda and Bivalvia, were identified bycollecting shells from the sea shores of Goa. Classification of shell specimen wascarried out following standard taxonomic literature on binomial classificationusing several guides, manuals and websites (Abott and Dance 1982, Apte 1986,Apte 2014, Bosch et al. 1995, Carpenter and Niem 1998, Dance 2002, Fiene-Severnset al. 1998, Harasewych and Moretzsohn 2010, Mollusca base 2016, WoRMSEditorial Board 2016. No live animals were killed, harmed, injured or displaced fromtheir habitats for this study.

1.5 Classification of Molluscs Based on Shells 9

1.7 Shells of Class Gastropoda

The following section describes identification of shells of different familiesbelonging to Class Gastropoda and that were recorded in Goa.

1.7.1 Structure and Description of a Gastropod Shell

Gastropod shells (Fig. 1.5) are generally tubes or cones that coil around a centralaxis. One complete turn or 360° rotation of a gastropod shell in a spirally arrangedmanner is called as a whorl. The main parts of the shell are a spire and a bodywhorl. The protoconch or the early larval whorl forms the apex of the spire, whichconsists of all whorls except the body whorl. The spire height is an importantcriterion in identifying shells. The body whorl is the last formed whorl. Shape of thebody whorl helps in identification of the shell. These overlapping whorls connectwith a clear visible continuous line or indentation from the apex of the shell to theaperture, which is called as suture. Positioning, patterning, sculpture and colour ofthe suture provide valuable clues in identification. The angulation of the shell at orjust below suture is termed as shoulder of the shell. The angle at the shoulder maybe simple or keeled and may display ridges, spines or nodes. Ornamentation such asridges on the shell may be spiral, i.e. in the transverse direction or axial (or radial),

Apex

Spire

Body whorl

Whorl

Sculpture (Nodules) Suture

Posterior canal

Aperture

Outer lip

VaricesRibs/Ridges

Anterior canal

Fig. 1.5 Structure of a gastropod shell

10 1 Molluscs and Their Shells

i.e. in the vertical direction. Row of spines or nodes may form varices in someshells. Main opening of the shell from where foot and head emerge is called asaperture. The hard structure used to close the aperture is called operculum. Thecentral axial pillar of the shell around which the shell rotates is Columella. In somespecies, columella may have plicae or folds. The shells show an outer and an inner(columellar) lip, which may be continuous or divided by an anterior notch. Part ofthe inner lip behind Columella is referred as parietal. An anterior siphonal canal is atube or an extension of the aperture and is used for discharge of waste products.A posterior canal may be present. A hollow space near columella opening out in theanterior part of the shell is called umbilicus.

1.7.2 Classification of Gastropoda

Each shell pattern is very specific to the particular species that synthesizes it. Hence,different species of gastropoda can be identified from the type of shells that theysecrete. Initially, the shape of the shell and some salient features can help to placethe species in a particular family or families (Fig. 1.6).

Patellidae: These are true limpets having flattened or slightly elevated shells. Theyare either smooth or radially ribbed from outside and smooth inside with ahorseshoe-shaped muscle scar. The permanent scar is left at the point of attachmentto the rocks. These cap shaped shells help animals cling tightly to rocks and towithstand wave action.Fissurellidae: These keyhole limpets derive their name from the slit that they haveon their anterior margin. They have small cap-shaped, moderately elevated, ribbedshells with an apical hole. They have a horseshoe-shaped muscle impression on theinner side of the shell.Trochidae: These top shaped shells are colourful outside with granulated surfaces.Inner side of the shell is lined with mother of pearl. The shells have low spires withinflated whorls. Many have tubercles that are often joined displaying a beautifulpattern of beaded appearance on the outer side of the shell.Turbinidae: The turban shells have variable shapes such as conical, rounded orspherical and look like turbans. They may be smooth or sometimes stronglyornamented. They have a thick, heavy, calcareous operculum with curved ridges.Inner side of the shell is pearly with a round aperture. Turban shells mostly occur inwarm tropical waters, most often around coral reefs.Neritidae: Shells of Neritidae or nerites are thick, short spired with large bodywhorl. The spire is generally depressed. They have a thickened outer lip, which isoften toothed and helps in further identification of species. There is no umbilicus.Mouth of nerites is ovate or horseshoe-shaped. Nerites are found on rocky shores oramong mangroves.Cerithidae: Ceriths are moderately small conical shells with tall spire. They aremost abundant in shallow waters and are among the most common species of

1.7 Shells of Class Gastropoda 11

Class Gastropoda

Cap Top Conical Corkscrew Spindle Globose Ovate Barrel Pear Club

PatellidaeFissurellidae

Trochidae Turbinidae

Potamidae Cerethidae Conidae

Turritelidae Turridae

Strombidae Ranellidae Bursidae OlividaeMitridae

Neritidae Naticidae

Cypraeidae LittorinidaePlanaxidae Buccinidae Nassaridae

Babylonidae Melongenidae Muricidae

Various shapes of the shells

Cap

Patellidae

Fissurellidae

True limpets, radially ribbed from outside and smooth inside with a horse shoe shaped scar

Moderately elevated apex, ribbed shell with a hole on its anterior margin

Top

Trochidae

Turbinidae

Look like a top with a highly inflated body whorl; Ornamented with tubercles giving a beaded appearance

Well developed spires and whorls giving a turban like look.

Conical

Potamidae

Cerethidae

Conidae

Solid, thick, tall shell with many whorls Dull colored lacking attractive ornamentation

Moderately small sized shell with tall spireAttractively banded with variable sculpture

Inverted conical shape with low and flat spire, smooth surface A siphonal notch or an anterior canal and a fasciolar band presentFlattened whorls

Corkscrew

Turritelidae

Turridae

Slender, tall with pointed spireNumerous whorls with well defined sutures Spiral ribs is the only sculpture

Long siphonal canal, Rounded V shaped turrid notch present at the upper end of the outer lip Axial or spiral sculpture may be present

Spindle

Strombidae

Olividae Short spire with a channeled suture, smooth and glossy shells Callused columella

Conch shell with a flaring outer lip A stromboid notch at the front end of the outer lip

Sculptured with varices, spiral ribs, ridges and nodulesProminent varices on either sides, Short siphonal canal

Ranellidae

BursidaeCoarsely ornamented with knobs, warts, tubercles and nodulesTwo canals present Posterior anal canal distinguishes bursids from ranellids

Smooth or spirally sculptured, Narrow aperture, columellar folds, A notch for the siphonal canal, outer lip lacks lirae or teeth

Mitridae

Globose

Neritidae

Naticidae

Depressed spire Toothed and thickened outer lipOvate or horse shoe shaped mouth

Large half moon shaped aperture Thick callus present

Ovate Cypridae Solid thick shell with an inflated body whorlWell developed apertural teethBoth lips dentate and curved inside

Barrel Babylonidae Moderately sizedModerate spire with deep suture White colored with brown prominent blotches

Pear

Planaxidae

Buccinidae

Small but thick shellModerate spireWell marked siphonal canal

Tall spire with well defined sutureLarge inflated body whorlBrightly coloured with spiral bands

Strong spiral and axial folds Short and broad siphonal canal

Solid shell Well defined spire with shallow sutures

Littorinidae

Small size, glossyStrong vertical ridges and prominent axial ribs

Nassaridae

Club/Mace

Melongenidae

Muricidae

Large in size Moderate to low spire Broad siphonal canal Nodules and spiral ribs on all whorls

Beautifully sculptured with a variety of elegant ornamentationLong and tubular siphonal canal Outer lip often denticulated

Fig. 1.6 Charts for classification of gastropoda

12 1 Molluscs and Their Shells

gastropods in shallow waters. Though ceriths are found in all waters of the world,greatest concentration is in the Indo-Pacific zone. They may not be very colourful,but are attractively banded. They have variable sculpture, but most often havetubercles, axial ribs and very rarely short spines. Most species are intertidal foundamong mangroves or near coral reefs.Turritellidae: These screw shells are slender, tall with pointed spire. Though theyhave dull colours and no attractive ornamentation, members of Turritellidae arenoticed for their strikingly slender and generally long shells. The shells havenumerous whorls with well-defined sutures. Colours range from white, cream todark brown. Spiral ribs are the only sculpture the shell has and often, number andpattern of spiral ribs on whorls is a characteristic feature of different species. Thereis no umbilicus. These species are found in sandy places of the world.Planaxidae: Planaxis shells are tropical water snails comprising a few species.Shells are small, thick and bulbous. They have a moderate spire. They may besmooth or spirally ribbed. They have a distinct siphonal canal. They resemble snailsof Littorinidae, but can be distinguished from their well-marked siphonal canal.Shells are found on intertidal rocks.Potamididae: Shells of Potamididae or horn shells are found in mangroves ormudflats. The shells are solid, thick and heavy, but dull coloured and lack attractiveornamentation. They are tall shells having many whorls with spiral ribs andtubercles. The highest diversity of Potamididae is found in tropical Indo-Pacificregion.Littorinidae: Shells of Littorinidae are called periwinkles and are found in warm aswell as cool waters. They are solid shells, often found on rocky or mangrovesurfaces. They have well-defined spire with shallow suture. There is no umbilicus.Operculum is thin and corneous.Strombidae: Strombs are conch shells having a flaring lip. The shells are colourful,thick and heavy. Apart from flaring lips, another most prominent feature of strombsis the stromboid notch towards the front end of the outer lip. They live mostly inshallow waters, in sand, mud or reef. Species belonging to Genera Strombus have aflaring lip, spider conchs or Lambis genera have fingerlike projections while tibiasare spindle-shaped with long siphonal canal. Originally part of Strombidae, GenusTibia is now included in the family Rostellaridae.Cypraeidae: Cypraeidae shells or cowries are preferred by shell collectors for theirattractive colours, beautiful designs and glossy surface. Most cowries are ovate inshape, but they differ widely in their colour, size, and pattern. The cowrie shell isnormally solid, thick with an inflated whorl and has well-developed apertural teeth.Both the lips are dentate and normally curved inside. Cowries are normally found incoral reefs or rocks, abundant in tropics.Naticidae: Shells of Naticidae or moon shells are globular in shape. The aperture islarge and is half-moon-shaped. Hence, they are commonly called as moon shells.They have a short or flat spire and a large body whorl. Suture, if present, may beshallow. Most often, a thick callus is present, which may cover the umbilicus.Bursidae: Bursids or Frog shells are moderate to large sized, thick and heavy;fusiform (spindle-shaped) and are coarsely ornamented with knobs, warts, tubercles

1.7 Shells of Class Gastropoda 13

and nodules. Hence they are called as frog shells. Some may have spines or varices,diametrically opposite varices may be present on the whorls. Bursids generally havetwo canals located at anterior and posterior ends of the aperture; an anteriorsiphonal canal and the other posterior anal canal. The gutter-like canal at its rare endor the posterior anal canal distinguishes them from tritons of Ranellidae.Ranellidae: Shells of Ranellidae or tritons are moderate to large sized, thick andsolid. The shape is fusiform (spindle shaped). They have a tall spire and a largebody whorl. The shell is generally well sculptured with varices, spiral ribs/ridgesand nodules. Most species have prominent varices on either side of the shell,columellar folds, and teeth or folds on the outer lip. Siphonal canal is generallyshort. Posterior anal canal is absent.Buccinidae: Shells of Buccinidae differ widely in size from small to large, globose,conical or fusiform in shape. The family includes whelks and goblet shells. Theygenerally have tall spire with defined sutures and a large, inflated body whorl. Theyare generally brightly coloured with spiral bands, strong spiral ribs and axial folds.Siphonal canal may be short and broad.Nassariidae: The family includes colourful nassa mud snails and dog whelks.These are widely distributed and well represented in tropics. Most species preferwarm, shallow waters of intertidal mudflats. Nassa shells are small in size, glossyand differ widely in ornaments and colours. Nassa species are generally identifiedby presence of strong vertical ridges and prominent axial ribs on the shells.Melongenidae: Melon conchs of Melongenidae, a small family found in shallow,brackish intertidal waters of the world are best represented in mangroves andmudflats of tropics, though some species are found in temperate waters. The shellsare large in size, may be generally smooth or at times spiny. Some of the largest sizeshells of the world belong to Melongenidae. They generally have moderate to lowspire, but some species may have a tall spire. Body whorl is large. They have abroad siphonal canal. Melon conch shells are normally ornamented with nodulesand spiral ribs on all whorls.Muricidae: Members of Muricidae may be found in all waters but are abundant intropical waters near coral reefs. Murexes are beautifully sculptured and display avariety of ornamentation such as spines, tubercles, frills and varices. Though theyare generally not colourful, some of them are preferred by shell collectors for theirelegant ornamentation. The shells range from small to large sized, smooth toelaborately ornamented, thick and heavy to delicate and fragile. Outer lip is oftendenticulated. Siphonal canal, in some species, may be short and broad, but isgenerally long and tubular.Olividae: Olividae have two sub-families, Olivinae or Ancillinae. Shells of Olividaeare smooth, glossy and highly polished. The shells are oblong and fusiform orspindle-shaped. The spire is short with a channelled suture. The aperture is long.Olive shells have a callused columella with prominent folds. Ancillas have a thickcallus, which envelops spire. The shells may be of golden brown, orange andreddish colours. They also have an ancillid groove below the centre of the bodywhorl, below which there are two bands, an ancillid band and a fasciolar band.Columella may be smooth but twisted.

14 1 Molluscs and Their Shells