CALIFORNIA STATE UNIVERSITY, NORTHRIDGE THE EXTE~~AL MORPHOLOGY, fu~ATOMY AND LARVAL \l DEVELOPMENT OF SI!v!NIA AEQUALIS AND OF SI!V!NIA BARBARENSIS (GASTROPODA: PROSOBRANCHIA) A thesis submitted in partial satisfaction of the requirements for the degree of Master of Science in Biology by Kevan L. Main / January, 1980 The Thesis of Kevan L. Main is approved: _:Dr. Ross Pohlo Dr. Earl Segal, Chdirman California State University, Northridge ii ACKNOWLEDGEMENTS I thank Dr. Earl Segal for introducing me to marine biology and especially to the family Ovulidae. I am grateful for his help and interest in this thesis and for his careful editing of my manuscript. I also thank Dr. Ross Pohlo and Dr. Jim Dole for their help and encouragement during my graduate career. I am deeply indebted to Janice Johnson. Without her technical assistance, daily laboratory work in the larval culture experiments and constant encouragement this research could not have been completed. I am especially grateful to Roger Smith for his .Photography of the adult snails, technical assistance, careful editing of my manuscript and most important his moral support throughout my graduate career. Throughout this research I received assistance from many individuals and I am deeply grateful to each of them. I would like to thank Dr. James Vallee, Dr. Kevin Daly, Jim Walker, Marc Rosenthal, Dave Gomberg, Mary Jane Teiman, Rosalyn Kutchins, Pat LaFollette, Richard Chao, Dr. James McLean, Dr. Erik Hockberg, Dr. Joseph Moore, Dr. Steven Oppenheimer, Dr. Anthony Gaudin, Dr. Peter Bellinger, and Lee Baresi. iii TABLE OF CONTENTS Page Acknowledgements iii List of Tables v List of Plates vi Abstract viii Introduction 1 Materials and Methods 5 Results 10 Discussion 20 Literature Cited 26 Appendix: Plates 1-19 30 iv LIST OF TABLES Page Table 1: Characteristics of egg masses of Simnia aequalis and~· barbarensis. ... 10 Table 2: Size dimensions of larval stages of Simnia aequalis and S. barbarensis ...... 12 Table 3: Mean time, in days, to reach each developmental stage . .13 Table 4: Mean time, in days, to hatching .... 15 Table 5: Survival time, in days, after hatching of Simnia aequalis and S. barbarensis ..... 17 v LIST OF PLATES Page Plate 1: Egg mass with egg capsules of Simnia aequalis on the gorgonian Lophogorgia rigida . 30 Plate 2: Egg mass with egg capsules of Simnia barbarensis on the skeletal axis of the sea pen Acanthoptilum gracile . 32 Plate 3: Early trochophores of Simnia aequalis and of Simnia barbarensis . 34 Plate 4: Late trochophores of Simnia aequalis and of Simnia barbarensis . 36 Plate 5: Veligers of Simnia aequalis and of Simnia barbarensis . 38 Plate 6: Photomicrographs of veligers of Simnia aequalis and Simnia barbarensis . 40 Plate 7: Empty egg capsules and exit hole on egg capsules of Simnia barbarensis . .... 42 Plate 8: View showing granular shell sculpturing on the veliger shell of Simnia barbarensis and of Simnia aequalis . 44 Plate 9: View showing shell edge on the veliger shell of Simnia barbarensis and of Simnia aequalis . 46 Plate 10: View showing shell lip and ridge along columellar base on the veliger shell of Simnia barbarensis and of Simnia aequalis 48 Plate 11: View showing shell surface of adult Simnia aequalis . 50 vi LIST OF PLATES, CONT. Page Plate 12: View showing mantle projections on adult Simnia aequalis and gorgonian polyps on Lophogorgia rigida . ..... 52 Plate 13: View showing ventral surface of adult Simnia aequalis . 54 Plate 14: Adult female of Simnia barbarensis showing contents of mantle cavity ....... 56 Plate 15: Adult male of Simnia barbarensis showing contents of mantle cavity ....... 58 Plate 16: View of adult Simnia barbarensis on the sea pen, Acanthoptilum gracile ........ 60 Plate 17: View showing mantle on Simnia barbarensis .... 62 Plate 18: Transverse row of teeth from the radula of Simnia barbarensis and Median tooth of Simnia aequalis . 64 Plate 19: View of Simnia barbarensis feeding on the sea pen, Acanthoptilum gracile ...... 66 vii ABSTRACT THE EXTERNAL MORPHOLOGY, ANATOMY AND LARVAL DEVELOPMENT OF SIMNIA AEQUALIS AND OF SIMNIA BARBARENSIS (GASTROPODA: PROSOBRANCHIA) by Kevan L. Main Master of Science in Biology The members of the family Ovulidae are always found living on cnidarian hosts, usually alcyonarians. The colors of the shells tend to blend with the host on which they are found being purple on purple gorgonians or yellow on yellow gorgonians. Simnia aequalis lives on the gorgonian Lophogorgia rigida in the northern Gulf of California. S. barbarensis lives on the sea pens, Acanthoptilum gracile, Ptilosarcus gurneyi and the gorgonian, Lophogorgia chilensis in Southern California. viii External morphology, mantle cavity and radula of Simnia aequalis and of S. barbarensis are described and compared to those of other members of the family Ovulidae. Larval development of both species was studied through laboratory culture over a one-year period. Development of S. aequalis is compared to that of S. barbarensis. This work is related to other researchers descriptions of the larvae of S. spelta and~· patula. Planktotrophic larval culture in a closed seawater system was carried out and the problems are discussed. Feeding behavior of adult snails was observed and is described. ix INTRODUCTION The members of the gastropod family Ovulidae are distributed throughout the world seas; however, they are most concentrated on the west and east coasts of Australia, the Philippines and Japan. The taxonomy of this group has been revised many times (Cate, 1969, 1973, 1974; Schilder, 1968, 1971) and is currently in a state of confusion (James McLean, personal communication). Very few species occur sympatrically (Cate, 1969) and they are always found living on cnidarian hosts, usually alcyonarians (Abbott, 1968; Cate, 1969, 1973; Hyman, 1967). The colors of the shells tend to blend with the host on which they are found being purple on purple gorgonians or yellow on yellow gorgonians (Hyman, 1967; Keen, 1971; Osburn, 1885). The mantle which covers and protects the smooth shell also blends with the host and may bear small white projections which resemble the host polyps (Abbott, 1968; Patton, 1972; Theodor, 1967). The adaptive coloration of the mantle and shell of ovulids has caused observers (Abbott, 1968; Keen, 1971; McLean, 1978; Robertson, 1970) to assume that the snail is feeding on the host alcyonarian. The relationship between some ovulids and their hosts has been studied. According to Lebour (1932), Simnia patula feeds on the alcyonacean, Alcyonium digitatum and the gorgonian, Eunicella verrucosa. Further Simnia spelta feeds on the host coenenchyme and may denude portions of branches of Eunicella stricta (Theodor, 1967). Berrill (1966) shows a photograph of Cyphoma sp. removing the coenenchyme of 1 2 Pseudopterogorgia sp. and Robertson (1970) states that both Jenneria pustulata and Pedicularia decussata feed on stony corals. However, Patton (1972) found no indication that living tissue of the gorgonian, Leptogorgia virgulata, was ingested by Neosimnia uniplicata but rather that the snails were feeding on thin sheets of mucus containing spicules shed by the host and material that settles on the colony. The placement of members of the family Ovulidae into species is based entirely on shell characteristics (Berry, 1916, 1946; Cate, 1969, 1973). In 1923 Vayssiere did the only anatomical description of the genus Simnia. He described the radula and general anatomy but ignored the reproductive system of several Atlantic and Mediterranean species. Later Ghiselin and Wilson (1966) described the anatomy and reproductive system of Cyphoma sp., a related Caribbean ovulid. The development of Simnia has been examined in Simnia patula (Lebour, 1932) and Simnia spelta (Thiriot-Quievreux, 1967). The larval descriptions of .§_. patula are based on plankton collected off the coast of England. Lebour feels that a long larval life is indicated in .§_. patula because the late larval stages lived for several weeks in a plunger jar without loss of the velum. In addition, .§_. patula has long velar lobes, a characteristic of long-lived gastropod larvae e.g. Nassarius incrassatus. The larval descriptions of.§_. spelta seem to be primarily based on plankton collected in the Mediterranean and on larvae Thiriot-Quievreux was 3 able to raise for short periods of time in the laboratory. She neither mentions how long she was able to keep the larvae alive nor the method of maintenance of the various stages in the laboratory. Thiriot-Quievreux estimated the larval life of S. spelta to be two to three months. Both S. patula and ~· spelta have planktotrophic larvae. Prosobranchs with planktotrophic larvae have been successfully reared through metamorphosis in the laboratory. They include the mesogastropods Littorina picta (Strusaker and Costlow, 1968, 1969) and Crepidula fornicata (Pilkington and Fretter, 1970) and the neogastropods Nassarius obsoletus and N. vibex (Scheltema, 1961, 1962a, 1962b), Strombus gigas (D'Asaro, 1965) and~· gigas, S. costatus and~· pugilus (Brownell, 1977). The main difficulties encountered in culturing planktotrophic larvae are: 1. lack of an appropriate food, 2. parasites and 3. lack of a proper stimulus to trigger matamorphosis (Franz, 1975). Simnia aequalis Sowerby lives on the gorgonian Lophogorgia rigida in the northern Gulf of California. Simnia barbarensis Schilder lives on the sea pens, Acanthoptilum gracile, Ptilosarcus gurneyi and the gorgonian, Lophogorgia chilensis (Los Angeles County Natural Museum collection and James Vallee, personal communication) in Southern California. The only information available on these two simniids was the shell descriptions in Berry (1916), Cate (1969, 1973) and Sowerby (1848). 4 This study has four objectives. First, to describe the development of Simnia aequalis and ~· barbarensis from egg through the planktotrophic larval stage. Second, to compare the develop­ ment of S. aequalis and S. barbarensis. Third, to develop a method for rearing both species in the laboratory. Last of all, to describe the external morphology, contents of the mantle cavity and radula of the adults of each species.