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 (: 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 . 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 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 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 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 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 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), feeds on the alcyonacean,

Alcyonium digitatum and the gorgonian, 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 sp. removing the coenenchyme of

1 2

Pseudopterogorgia sp. and Robertson (1970) states that both

Jenneria pustulata and 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 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 (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. MATERIALS AND METHODS

Collection, maintenance and preservation of adult

Simnia aequalis were collected at the mouth of Estero Morua, located approximately 5 km south of the University of Arizona-

University of Sonora Environmental Research laboratory in Puerto

Penasco, Sonora, Mexico (31.20N, 113.35W). The yearly water temperature range in Puerto Penasco is from 15°C to 30.6°C

(Robinson, 1973). Specimens were collected on extreme minus tides along with their gorgonian hosts, Lophogorgia rigida, in

September 1978 and January 1979. ~· aequalis were maintained with their gorgonian hosts in recirculating natural seawater systems in two temperature regimes, 14° ± 1°C and 26° ± 1.5°C. Two temperatures were used to determine if temperature influenced egg laying. Gorgonians were fed brine shrimp nauplii three times each week. Each aquarium and gorgonian colony was checked daily for deposited egg masses and for total number of snails. 1 Simnia barbarensis were collected by SCUBA divers at depths of 4.6 to 9.1 M in the main exit channel of Mission Bay, California,

U.S.A. (32.46N, 117.14W) on the sea pen, Acanthoptilum gracile in

January 1979. The yearly water temperature range in Mission Bay is from 13.9°C to 20.6°C (U.S. National Weather Service).

S. barbarensis were maintained in recirculating natural seawater

1. Pacific Bio-Marine Supply Co., P.O. Box 536, Venic.e, California 90291

5 6

0 0 at one temperature, 11 ~ 1 C. These snails were offered fresh

A. gracile weekly and each A. gracile colony was checked daily for deposited egg masses.

Simnia aequalis and ~· barbarensis were identified with the assistance of Pat LaFollette, Los Angeles County Natural History

~ruseum, Department of Malacology. Specimens have been placed in the museum collections for future reference.

Adult snails of both species were prepared for dissection by relaxing them in 3% alcoholized seawater and placing them in Bouin-

Duboscq solution for 48 hours. Specimens were then washed in 70% ethyl alcohol. were prepared for examination according to the techniques of Hackney (1945).

Rearing conditions Thousand ml Pyrex beakers covered with loose glass l:i.ds were used as rearing containers for the egg masses and larvae. Each beaker was washed in detergent, distilled water and autoclaved prior to its use to prevent any contamination (Allen and Nelson,

1908). All seawater was collected at least 8 km off the

Southern California, U.S.A., coast in the Catalina channel, to avoid possible sewage contamination. The seawater was sterilized in an Aquanetics Ultra-Violet sterilizer to prevent bacteria and fungus from entering the cultures (Loosanoff and Davis, 1963).

After UV treatment, the water was filtered through W.H. Curtin and

Co. qualitative filter paper #7760 to remove any suspended particles. 7

The egg masses were maintained in 250 ml seawater and the water

was changed daily until hatching. After hatching the larvae were

removed by straining through 72M Nytex mesh netting. This netting

trapped the larvae so they could be transferred into a clean beaker.

The larvae were maintained in 950 ml seawater with antibiotics and

the water was changed every two days. Both Streptomycin sulfate

and Neomycin sulfate were added in a concentration of .1 g/1. The

combination of these antibiotics has controlled bacterial growth

in bivalve culture (D'Agostino, 1975).

Th e 1arvae were grown a t 14 0 : 10 C and 18 0 ± 3 0 C. Two

temperatures were used to determine which produced the fastest

growth and maximum survival. Simnia barbarensis lives in water

which is less than 16°C during most of its life. For this reason data presented in the text will be for the larvae raised at 14°C

unless otherwise stated. The length of time to reach the developmental

stages at both 14°C and 18°C is given in Table 3. T-tests were

performed to determine if there was a significant difference

(~< 0.05) in the rate of development between the two species and between the two temperatures.

Continuous illumination from General Electric "Cool White" fluorescent tubes was used for all cultures. Pilkington and

Fretter (1970) found that larvae showed better growth with constant illumination than with alternating 12 h periods of light and dark.

Four different food combinations were fed to larvae to determine which would give optimum growth and survival conditions. 8

Larvae were fed either:

1. Monochrysis lutheri Droop (Order Chrysophyceae)

2. Isochrysis galbana Parke (Order Chrysophyceae)

3. Monochrysis lutheri and Isochrysis galbana

4. Phaeodactylum tricornutum Bohlin (Order Bacillariophyceae).

Algal foods were maintained in Erdschreiber solution

according to the techniques of James (1969) and Schlieper (1972). 4 Food concentrations were kept at 10 cells per ml and measurements

of culture growth were made with a haemocytometer. Some larvae

were fed 4 ml and stirred daily while others were fed 4 ml and

stirred every other day to determine which procedure allowed

for optimum growth. Stirring the culture oxygenates the water

and suspends the food in the beaker.

Observation techniques

Egg masses were examined daily with a dissecting scope and

the developmental stage of each was noted. When at least two

capsules within one egg mass were observed to contain larvae which

had changed into the next larval stage, that egg mass was declared

to have reached the next stage. Larvae were measured using a micrometer on a compound Wild research microscope. Drawings were

usually made with the aid of a camera lucida on either a dissecting

or compound microscope. Photomicrographs were also taken of the veligers of both species with a 35 mm Zeiss IKON camera on a Zeiss research microscope (50.4 magnification). Scanning Electron

Microscope (I.S.I. SEM-II, Model SMSM) photographs were taken of 9

I • veliger shells at hatching. Specimens were preapred by soaking in 70% bleach for two days to dissolve the tissue and transferred to the SEM stub in a drop of water. The water was then removed and the specimens were allowed to dry for two days. The adhesive used was polylysine. Adult specimens were photographed with a

35 mm Olympus OM-1 with autobellows and reversed 50 mm, f 1. 4,

Zuiko lens.

Many gastropod larvae exhibit photopositive behavior immediately after hatching and later exhibit photonegative behavior prior to settlement and metamorphosis (Chia and Koss,

1978) . The larvae were tested for photoresponse by shining a beam of light at the side of the beaker. RESULTS

Egg Capsules

Simnia aequalis laid their eggs in round gelatinous capsules

on the branches of the gorgonian, Lophogorgia rigida. Many

capsules were laid at one time and a group of joined capsules was

called an egg mass. Capsules were joined to each other by a

fibrous layer of membrane (Plate 1) which was colorless and

transparent. The branches of L. rigida were not damaged by the

egg mass; following hatching the mass fell off the gorgonian and the previously covered polyps resumed feeding. The capsules were white and transparent, allowing the eggs to be seen through the albumen membrane. Of 53 egg ma~ses examined, the number of capsules varied between 6 and 40 with a mean of 17. 7. The mean vol·ume of the

egg capsules was 0.209 ml and the volume available to one egg within a capsule was 0.011 ml. The number of eggs per capsule varied between 131 and 280 (Table 1). ~· aequalis laid their eggs year round, both in the laboratory and in the field. Gorgonians with egg masses present were collected in September, January, March and

April at Estero Morua. Table I· Charac~eristics of egg masses of Simnia aequalis and S barbarPnsis-

Mean number of Mean number of ~lean volume of Mean volume available to Species egg capsules per eggs per capsule egg capsule one egg per capsule egg mass

3 s. aegua!is 17.7 t 0.95 (53)b 198.4 ! 27.86 (S) 0.209 ml (8) 0. 0011 ml

s. barbarensis 47.6 t 7.29 (16) I 63d.2 t 8.60 (S) 0.550 ml (8) 0.0087 ml

a. + Standard Error b. ~umber of units examined

10 11

Simnia barbarensis laid their eggs in oval shaped capsules on the stripped skeletal axis of Acanthoptilum gracile. The capsules were also laid in an egg mass which was joined by a fibrous layer of membrane (Plate 2). Capsules were white and transparent, as were those of S. aequalis. Of 16 egg masses examined, the number of capsules varied between 11 and 107 with a mean of 47.6. The mean capsule volume was 0.55 ml and the volume available to one egg within a capsule was 0.0009 ml. The number of eggs per capsule varied between 610 and 651 (Table 1). In the laboratory

S. barbarensis laid their eggs for a seven month period beginning in February and ending in late August. Field collections of sea pens were made in January, February and June; egg masses were present only in June.

The capsules of Simnia barbarensis were larger than those of

S. aequalis; however, ~· barbarensis laid many more eggs than

S. aequalis. The total capsule volume available to one egg in a capsule was slightly more for~· aequalis. Consequently, the eggs of S. barbarensis were more crowded within a capsule than those of S. aequalis.

Larval Development

Simnia aequalis and S. barbarensis pass through four developmental stages inside the egg capsules. In the first stage the eggs undergo cleavage divisions and pass through the blastula and gastrula stages. Eggs of both species were opaque white during this period. There was no noticeable movement and the eggs were suspended in albumen. Table 2: Si:z.e dimensions of larval stages of §._imni~ ~ualls and ~· barbarensis

Early Trochophorcs Late Trochophores Veliger Shells Specles (in A"') (in J.'.m) (in J\111) (In .Ant) (in Am) (in JJ.IIl) Length Width l.eugth Width Length Width

3 ~· aC

-S. barbarensis 142.5:!:2.50 (4) ll9.8t3.40 (4) 124.9:!;4.52 (10) 101.9~5.44 (tO) 144.4~1.52(16) 107.0:!:2.12 (16}

a. :!; Standard fln:or b. number of larvae measured

...... N 13

Following the gastrula is the early trochophore stage, which occurred 7.9 days (mean) after laying in Simnia aequalis and 11.2 days (mean) after laying inS. barbarensis (Table 3). S. barbarensis was significantly larger than ~· aequalis in this stage. The mean length and width were 129.7fi and 113.5~, respectively, in~· aequalis while they were 142. 5_;.( and 119. 8_1-{ in ~· barbarensis (Table 2).

Larvae of both species were oval, whitish-colored, transparent balls which were much larger than the gastrula stage. If the capsule was broken, releasing the trochophores, they turned opaque white.

Early trochophores possessed an apical plate and tuft (Plate 3).

The larvae appeared to move continuously. Except for the trochoblasts, which were large in ~· aequalis, larvae of both species were very similar (Plate 3 A and C) .

Early trochophores developed into late trochophores within three to four days. Although Simnia barbarensis were larger than

~· aequalis in the late trochophore stage this difference was not significant. The mean length and width were 122.3;.< and 91.6..u.. , respectively, inS. aequalis, while they were 124.9_..M and 101.9)-A..

Table 3: ~lear. time, in days, to reach each developmental s-cage

i Tempera-eure Species I Early La.o:e Veliger I Trochophore Trochophore I oc I I i aequalis O.. Z2a (14) b I i s. 7.9 - 11.1 : 0.30 (14) 15.9 ! 0 • .38 (12) I 14 I I s. barbarensis jn. 2 . 0.65 (6) 15.4 0.75 (5) 20~S 0.54 (6) I - : I ! ! 1 s. aequal ~s I 6.0 : 0.31 (15) S.4. . 0 . .31 (14) 11.7 ! 0.45 (14) 18 - I I I ba~barensis I I s. 8.0 ! 0.78 (8) ll. 0 0.98 (7) 13.7 . O.S8 (6) : I

a. : Standard Error

b. number of egg masses ex~~ined 14

in S. barbarensis (Table 2). Late trochophores, which were opaque

white in color, were more elongate and narrower than early trocho­

phores. Velar cilia were present along with the apical cilia, as

the velum began to develop (Plate 4), and both the shell and

operculum made their appearance. Late trochophores were very

similar in both species.

Veligers of both species were distinguished by the

presence of a developed velum and a light pink shell, which darkened to a pinkish-brown prior to leaving the capsule. The veliger stage began 15.9 days (mean) after laying in Simnia aequalis

and 20.5 days (mean) after laying in~- barbarensis (Table 3).

In the veliger the pink shell was somewhat transparent and the digestive gland could be seen through the shell. The foot and body of the veligers were white and they had two transparent, round, velar

lobes which were ciliated. The transparent operculum on the bottom

of the foot clearly showed the two statocysts found in the foot

(Plates 5 and 6).

Veligers left the egg capsules through a round off-centered hole on each capsule of an egg mass (Plate 7). This exit hole appeared to be a weak point on the capsule which was broken open by the force of the veligers as they continuously btooped into the capsule wall. Veligers hatched out of the capsules 24.6 days (mean) after laying in Simnia aequalis and 26.3 days (mean) after laying inS. barbarensis (Table 4). After leaving the capsule the veligers oscillated vertically in the water column. They neither became 15

entangled in the air-water surface film which is so common in opisthobranch veligers, nor did they respond photopositively or photonegatively. At hatching the larval shells of ~· aequalis had a mean length and width of 123.8A and 96.8~ , respectively, while those of S. barbarensis were 144.~ and 107.0~ (Table 2).

Veligers of S. barbarensis and S. aequalis were identical except in size. S. barbarensis veligers were significantly larger than those of S. aequalis.

Table 4: Mean time, in days, to hatching

Temperature Species Hatching oc

s. aequalis 24.6 + 1.08a (ll)b 14 s. barbarensis 26.3 :!: 2.19 (3)

s. aequalis 17.6 ± 1. 09 (12) 18 s. barbarensis 19.7 + 1.43 (6)

a. + Standard Error

b. number of egg masses examined

Scanning electron photomicrographs show that at hatching the veliger shells had a rough granular surface (Plates 8 and 9).

Simnia barbarensis possessed a thickened outer shell lip and a ridge along the columellar base. S. aequalis showed neither of those sculptural characteristics (Plate 10) . The outer lip of both species had a central tooth which separates the two sinuses supporting the velum. This central tooth was more prominent in

S. aequalis (Plate 9). 16

Larval Culture

Survival time varied with the feeding regime. Simnia aequalis survived longest on Isochrysis at 14 0 C and on Isochrysis and Mono- chrysis combined at 18 0 C (Table 5). S. barbarensis survived longest on Monochrysis at both 14°C and 18°C. No differences could be determined between the larval cultures which were fed daily and those which were fed every other day. Larvae in all cultures died before metamorphic competence was reached. In the larval cultures the presence of protozoan, nematode or copepod parasites could not be eliminated. The three parasites were often present in culture and were observed eating veligers on two occasions. Parasites were usually not seen on the egg capsules until the late trochophore or veliger stage was reached. Swimming veligers were often trapped in a filamentous algae which was present in many cultures and could not be controlled.

The larvae of both species developed significantly faster at

18 °C than at 14°C. At b o th t ernpera t ures s·1mn1a . aequa 1·1s passed through each stage significantly faster than S. barbarensis (Table 3).

S. aequalis hatched out of the capsules sooner than S. barbarensis at both temperatures, however, this difference was not significant (Table 4).

Adult Snails

Simnia aequalis ranged from 10 mm to 18 mrn in length and possessed a purple shell matching the coenenchyrne of its host,

Lophogorgia rigida. Numerous transverse incised striae were Table 5: Survival time, in days, after hatchiug of Sinmia aequalis and ~· ~rensi_~

Temperature Algfll Food Species oc Isochrysis ~lunochrysis I so. + Hono. Phacod~ctylum ~· aequalis 45.0 :!: oa (2)" 23.3 :!: 5.21 (3) 37.0 "!: 2.89 (3) 35.0 :!: 5.57 (3) 14 S. barbarensis 38.3 11.7 22.0 !: 2.0 - - ± (3) (2) 44.3 ± 5.17 (3) 48.0 "!: -- (1)

S. aequalis 36.5 "!: 5.20 (4) 40.6 :!: 2.35 (7) 42.0 "!: -- (I) 21.0 + 1.47 ( 4) lll S. barharcnsis (2) (1) + - 27.0:!: -- (1) 26.0 :!: 6.0 30.0 :!: -- 38.5 2.06 (4) ------· -- L--- - -~~-- ---

a. "!: Standard Error b. number of cultures

I-' -....! 18

present near the terminal ends but were obscure or absent on the central dorsum (Plate 11). In older animals (6 months to one year) the outer lip became thickened and lighter in color (sometimes white) than the rest of the shell. The columella-fossula area was also lighter than the rest of the shell (sometimes white) and smooth.

Shell tips were often yellow to orange; occasionally they were purple. A thin white mantle, which appeared purple due to numerous purple spots, usually covered the shell. The leading edge of the mantle had a purple border followed by a white strip with a row of purple spots. Purple splotches cover the remainder of the mantle.

Small white projections, resembling the white polyps on L. rigida, were on the mantle (Plate 12). Projections on a few snails were eight fingered matching the tentacles of the gorgonian polyps. The siphon and head were dark purple, while the tentacles were purple with white tips (Plate 13). The foot was dark purple on the sides and had numerous folds which gave a pleated effect. The ventral surface of the foot was white.

Simnia barbarensis ranged from 15 mm to 30 mm in length with either a pink, light-yellow or an ivory-colored, transparent shell closely resembling its host, Acanthoptilum gracile (Plate 16).

The surface was smooth and unlined and its outer edge was narrowly thickened. Shell tips were always light yellow. A thin white mantle, with many pinkish-brown splotches, usually covered the shell (Plate 17). Some snails had small yellow projections on the mantle surface. The sides of the foot may be white or yellow with 19

small pinkish-brown spots. The foot was pleated, as in~· aequalis,

and had a white ventral surface (Plate 16). The siphon and head

varied from white to yellow while the tentacles were whitish-yellow

with a pinkish-brown spot or tip (Plates 16 and 17).

Internally, the mantle cavity of Simnia aequalis and

S. barbarensis was elongate and shallow and greatly resembled

that of Cyphoma gibbosum (Ghiselin and Wilson, 1966). As found

in all Cypraeacea (Vayssiere, 1923), the osphradium was tripartite.

Posterior to the osphradium was a curved gill, which was slightly

anterior to the many folds of the hypobranchial gland (Plate 14).

The anus and genital openings were more posterior than those of most mesogastropods and the penis was caudal (Plate 15), as in

Cyphoma.

The intestines of both Simnia aequalis and ~· barbarensis

contained numerous spicules of their host organisms.

The radula of Simnia aequalis and of S. barbarensis was of

the taenioglossate type, consisting of seven teeth in a

transverse row; one central median tooth, flanked on each side

by one long, spear-shaped lateral and two marginals (Plate 18).

The median consisted of a large cusp in the center with several

smaller cusps on either side. The number of cusps on either

side was usually five (sometimes 4 or 6) in ~· aequalis and usually seven (sometimes 6 or 8) in S. barbarensis. Marginals were highly serate with many dentils on each. The number of dentils on the outer marginals varied from row to row in both species. 20

Simnia barbarensis stripped all the flesh off the skeletal axis of Acanthoptilum gracile and then laid their eggs on the cleaned surface (Plate 19). In contrastS. aequalis appeared to run their mouths over the surface of Lophogorgia rigida but not to feed on the polyps; the gorgonians always appeared to be intact and healthy. DISCUSSION

Egg capsules

Simnia aequalis lay their eggs in capsules which are nearly

identical to those of S. barbarensis. Other ovulids in the genera Simnia and Neosimnia whose egg capsules have been described

(~. patula, Lebour, 1932; ~· spelta, Thiriot-Quievreux, 1967; and

Neosimnia uniplicata, Patton, 1972) are similar to both those of

S. aequalis and S. barbarensis. All five species lay their eggs in capsules joined to each other by a fibrous layer of membrane.

The shape of the capsules differ slightly being round in some species and oval in others. This may be due to the "smoothness" of the surface upon which they are laid i.e. on branches of the host gorgonian. Other members of the family Ovulidae also lay their eggs in capsules which may be separate or joined together in an egg mass. However, the shape of the capsules are different from those of Simnia and Neosimnia. Both Trivia europa (Lebour,

1932) and Cyphoma gibbosum (Crovo, 1974) lay their eggs in vase-shaped capsules. It appears as though egg capsules which are round or oval in shape are characteristic of the genera Simnia and Neosimnia and not of other members of the family Ovulidae.

The branches of Lophogorgia rigida are not damaged by the egg masses of Simnia aequalis. Neosimnia uniplicata's egg masses also do not damage the branches of Leptogorgia virgulata (Patton,

1972). However, the egg masses of S. spelta (Theodor, 1967)

20 21

usually cause necrosis of the underlying tissue of its host,

Eunicella stricta. Cyphoma gibbosum lays its capsules after removing the coenenchyme of Muricea muricata (Cather and Crovo, 1972).

S. barbarensis lays its capsules only after removing the flesh of its host Acanthoptilum gracile. Simnia appears to require a hard surface on which to lay its egg mass and the only hard surface of A. gracile is its hard internal skeleton. Trivia europa

(Lebour, 1932) is associated with a compound ascidian which does not have a hard external skeleton. Trivia bites holes in the ascidian and lays its eggs in capsules within these holes.

Larval Development

Both Simnia aequalis and ~· barbarensis pass through four developmental stages prior to hatching and appear to follow the same developmental path. All previous investigators have ignored these larval stages so no comparisons can be made to other ovulids.

The veliger shells of both Simnia aequalis and ~· barbarensis are pinkish-bro\vn in color at hatching. Both~· patula and

S. spelta have a darker veliger shell at hatching. The shell of~· patula is dark-brownish in color (Lebour, 1932), while that of~· spelta is brownish-yellow in color (Thiriot-Quievreux,

1967). When the veligers of ~· patula are fixed in Bouin-Duboscq solution a film separates off the shell. Lebour presumed that it was the periostracum. Thiriot-Quievreux found no such analog in S. spelta. I did not find the accessory shell in either 22

~· barbarensis or~· aequalis. The velum of~· patula acquires

a dark brown border shortly after hatching. This is not present

in~· aequalis, ~· barbarensis or~· spelta.

Scanning electron photomicrographs reveal some structural differences in the veliger shells of Simnia aequalis and

S. barbarensis. These differences may prove useful in differ­

entiating one species from another.

Larval Culture

Temperature does affect larval growth rate. Larvae in the capsules develop significantly faster at 18°C than at 14°C,

_which is not surprising because of the effect of temperature which speeds up metabolic processes. Strusaker and Costlow

(1969) found that Littorina picta develops faster at higher temperatures than at lower.

On the experimental diets it appears as though survival time varied with the feeding regime. However, I am convinced that length of survival was not correlated with any particular food type. This statement is based on three factors: (1) The presence of parasites and algae appeared to be the major cause of larval mortality. Protozoan and nematode parasites caused high mortality while the larvae were inside the capsules.

They bored into the capsules and ate many of the larvae present. Since they were seldom seen until the larvae were in the late trochophore or veliger stage, it appears that they must have been present on the outside of the capsules 23

in an egg form and developed along with the larvae. Both types of parasites were not a problem after hatching. However, once the veligers hatched filamentous algae was the major cause of mortality; these algae appeared in many cultures and the larvae became tangled in them and died. In addition copepod parasites were frequently seen in the free swimming veliger cultures and were probably contributing to their mortality. (2) Both

Monochrysis and Isochrysis are excellent food sources for opisthobranch and bivalve veligers. Switzer-Dunlap and Hadfield

(1977) used both these algae in Aplysia culture and have found them to be highly successful. However, when Littorina picta

(Struhsaker and Costlow, 1969) and Crepidula fornicata

(Pilkington and Fretter, 1970) were fed Isochrysis and

Monochrysis the ve1igers survived but did not grow or reach metamorphic competence. Neither Simnia barbarensis nor ~· aequalis grew larger than 200ft during the course of the experiment.

At metamorphic competence ~· patula measured 800~ (Lebour, 1932) and~· spelta measured 500~ (Thiriot-Quievreux, 1967). Neither

Isochrysis nor Monochrysis produced sufficient growth of

~· aequalis and ~· barbarensis veligers for metamorphosis to occur. (3) Water quality may have contributed to the problems encountered with algae and parasites. Water was collected at least 8 km offshore, to prevent possible inshore sewage contamination, and was stored for upwards of two months. Stored seawater has a different chemical composition than freshly 24

collected seawater (King, 1975). James Vallee (personal communication) who conducted larval culture experiments with

Aplysia using seawater which had been stored for short periods of time (1 to 2 weeks), encountered the same algal and parasitic contamination problems as I did.

Adult Snails

According to Cate (1963, 1973) yellow or orange shell tips are a differentiating characteristic for Simnia aequalis. Among the snails I worked with some did have orange or yellow tips while others had purple tips. Furthermore, the terminal tips of S. barbarensis were often yellow to orange. Since the color of the shell is a highly plastic character which varies depending on the host cnidarian (Abbott, 1968; Keen, 1971) it is probably not a useful criterion for species differentiation.

The mantle cavity of Cyphoma sp. (Ghiselin and Wilson, 1966) is very similar to that of Simnia aequalis and~· barbarensis.

The only diff~rence is the more anterior location of the osphradium in the two simniids. The general anatomy of three simniids,

S. spelta, ~· purpurea and ovum (= ~· patula) was described and figured by Vayssiere in 1923. The mantle cavity of these species appears identical to that of S. barbarensis and ~· aequalis.

On the median radular tooth the number of cusps of either side of a central larger cusp is usually five in Simnia aequalis

(4 animals) and seven in~· barbarensis (4 animals). According to Vayssiere (1923) there are three smaller cusps in ~· spelta, six inS. purpurea and six to eight to S. patula. Possibly 25

the number of small cusps adjacent to the larger central cusp on the median radular tooth of simniids may prove useful in species identification. More information needs to be gathered on eastern Pacific ovulids to determine if this character does vary from species to species.

The assumption that all ovulids are eating host tissue

(Abbott, 1968; Keen, 1971; McLean, 1978; Robertson, 1970) may be incorrect. In several species, Simnia spelta (Theodor, 1967),

S. patula (Lebour, 1932) and Cyphoma sp. (Berrill, 1966), feeding has been observed while in others it has not. S. barbarensis feeds on its host Acanthoptilum gracile, however, it appears that ~- aequalis does not feed on Lophogorgia rigida. Many gorgonians have been observed shedding thin sheets of mucus

(Patton, 1972; personal observation). This mucus has an organic composition and contains many spicules, diatoms and other microorganisms. Patton (1972) proposed that Neosimnia uniplicata was feeding on the spicule-containing mucus shed by its host

Leptogorgia. He writes "this would account for the presence of spicules in the feces and for the lack of damage to the host."

~· aequalis also appears to be feeding on the spicule-containing mucus and not on its host Lophogorgia. LITERATURE CITED

Abbott, R.T., 1968. Seashells of North America. Golden Press, New York, 280 pp.

Allen, E.J. and E.W. Nelson, 1908. The rearing of marine larvae. J. mar. biol. Ass. U.K. 8: 464-473.

Berrill, N.J., 1966. The life of the ocean. McGraw-Hill, New York, 232 pp.

Berry, S.S., 1946. A new Californian Neosimnia. J. Conch. London 22: 29-35.

Berry, S.S., 1916. A new ovula from California. Nautilus, Boston Mass. 30: 21-22.

Brownell, W.N., 1977. Reproduction, laboratory culture, and growth of Strombus gigas, S. costatus and S. pugilus in Los Roques, Venezuela. BuTL Marine Sci. 27: 668-680.

Cate, C.N., 1969. A revision of the eastern Pacific Ovulidae. Veliger 12: 95-102.

Cate, C.N., 1973. A systematic rev1s1on of the recent Cypraeid family Ovulidae. Veliger lS(Supplement): 1-116.

Cate, C.N., 1974. The Ovulidae: A key to the genera and other pertinent notes. Veliger 16: 307-313.

Cather, J.N. and M.E. Crovo, 1972. The spawn, early development and larvae of Cyphoma gibbosum (Cypraeacea). Nautilus, Phi1ad. 85: 111-114.

Chia, F.S. and R. Koss, 1978. Development and metamorphosis of the planktotrophic larvae of Rostangea pulchra (: Nudibranchia). Marine Biol. 46: 109-119.

Crovo, M.E., 1974. Further notes and corrections concerning the spawn of Florida Cyphoma (Ovulidae). Nautilus 88: 53-55.

D'Agostino, A., 1975. Antibiotics in cultures of invertebrates. IN: Culture of marine invertebrate animals. W.L. Smith and M.H. Chanley (eds). Plenum Press, New York. pgs 109-136.

26 ~"

------~- 27

D'Asaro, C., 1965. Organogenesis, development and metamorphosis in the Queen Conch, Strombus gigas, with notes on breeding habits. Bull. mar. sci., 15: 359-416.

Franz, D.R., 1975. Opisthobranch Culture. IN: Culture of Marine invertebrate animals. W.L. Smith and M.H. Chanley (eds). Plenum Press, New York. pgs. 245-256.

Ghiselin, M.T. and B.R. Wilson, 1966. On the anatomy, natural history and reproduction of Cyphoma, a marine prosobranch gastropod. Bull. mar. sci. 16: 132-141.

Hackney, A.G., 1945. The radula of Mollusks. Mollusca 1: 43-48.

Hyman, L.H., 1967. The Invertebrates, Volume 6, Mollusca 1. McGraw-Hill Book Co., New York, 792 pp.

James, D.E., 1969. Unialgal Cultures. Carolina Tips. Carolina Biological Supply Co., Burlington, North Carolina.

Keen, A.M., 1971. Sea shells of tropical west America, 2nd edition. Stanford Univ. Press. Stanford, Calif., 1064 pp.

King, J.M., 1975. Recirculating System Culture methods for marine organisms. IN: Culture of Marine invertebrate animals. W.L. Smith and M.H. Chanley (eds). Plenum Press, New York.

Lebour, M.V., 1932. The larval stages of Simnia patula. J. mar. biol. Ass. U.K. 18: 107-115.

Loosanoff, V.L. and H.C. Davis, 1963. Rearing of bivalve mollusks. Adv. Mar. Biol. 1: 1-136.

McLean, J.H., 1969. Marine shells of Southern California. Los Angeles Museum (Sci. Ser. Zool.) 11: 1-104.

Osburn, H.L., 1885. Mimicry in marine ~lollusca. Science 6: 9-10.

Patton, W.K., 1972. Studies on the symbionts of the gorgonian coral, Leptogorgia virgulata (Lamarck). Bull. mar. sci. 22: 419-431.

Pilkington, M.C. and V. Fretter, 1970. Some factors affecting the growth of prosobranch veligers. Helgolander wiss. Meeresunters. 15: 128-134. 28

Robertson, R., 1970. Review of predators and parasites of stony corals with special references to symbiotic prosobranch gastropods. Pacific Sci. 24: 43-54.

Robinson, M.K., 1973. Atlas of Monthly mean sea surface and subsurface temperatures in the Gulf of California, Mexico. San Diego Soc. of Nat. Hist. Memoires.

Scheltema, R.S., 1961. Metamorphosis of the veliger larvae of Nassarius obsoletus (Gastropoda) in response to bottom sediment. Biol. bull. 120: 92-109.

Scheltema, R.S., 1962a. Pelagic larvae of New England intertidal gastropods. I. Nassarius obsoletus Say and Nassarius vibex Say. Trans. Amer. microsc. Soc., 81: 1-11.

Scheltema, R.S., 1962b. Environmental factors affecting the length of pelagic development in the gastropod, Nassarius obsoletus. Amer. Zool. 2: 445.

Schilder, F.A., 1968. The generic classification of . Veliger 10: 264-273.

Schilder, M. and F.A. Schilder, 1971. A catalogue of living and fossil cowries: taxonomy and bibliography of Triviacea and Cypraeacea (Gastropoda: Prosobranchia). Mem. Inst. Roy. Sci. Belg. 85: 1-246.

Schlieper, C., 1972. Research methods in Marine Biology. Univ. of Washington Press, Seattle, 356 pp.

Sowerby, G.B., 1848. Thesaurus Conchyliorum, or monographs of genera of shells. Ovulum. London 2: 467-484.

Struhsaker, J.W. and J.R. Costlow, Jr., 1968. Larval development of Littorina picta Philippi (Prosobranchia: Mesogastropoda) reared in the laboratory. Proc. Malac. Soc. Lond. 38: 153-160.

Struhsaker, J.W. and J.R. Costlow, Jr., 1969. The effect of some environmental factors on larval development of Littorina picta reared in the laboratory. Malacologia 9: 403-419.

Switzer-Dunlap, M. and M.B. Hadfield, 1977. Observations on development, larval growth and metamorphosis of four species of Aplysiidae (Gastropoda: Opisthobranchia) in laboratory culture. J. exp. mar. Biol. Ecol. 29: 245-261. ~ ~. ------

29

Theodor, J., 1967. Contribution a l'etude des gorgones VI. Le denudation de la branches du gorgonians mollusques predateurs. Vie et Milieu 18: 73-78.

Thiriot-Quievreux, C., 1967. Observations sur le development larvaire et postlarvaire de Simnia spelta Linne Vie et Milieu 18: 143-151.

Vayssiere, A., 1923. Recherches zoologiques et anatomiques sur les Mollusques de la famille des Cypraeides. Ire partie. Ann. Mus. Hist. nat. Marseille, 18: 1-120. 30

APPENDIX

Plate 1: Egg mass with egg capsules of Simnia aequalis on the gorgonian Lophogorgia rigida. Ab-Albumen, AM-Albumen membrane, E-eggs, FM-fibrous layer of membrane

32

Plate 2: Egg mass with egg capsules of Simnia barbarensis on the skeletal axis of the sea pen Acanthoptilum gracile. Ab-Albumen, AM-Albumen membrane, E-eggs, FM-fibrous layer of membrane W\f \~-----Q\f ~----3 34

Plate 3: Early trochophores of Simnia aequalis (A,B) and of Simnia barbarensis (C,D). Ap-Apical plate, AT-Apical tuft, SP-Shell primordium, Tr-Trochoblast A B

tf(jj~~--- AT ~rr.o----A p

0 .1mm

c D .•.• LVTr _____ AT ,,&JJ!'tftrr,;----AT ~~------.AP ~:Z:25it---AP ~~~~8----Tr (.N 0\

Plate 4: Late trochophores of Simnia aequalis (A-C) and of Simnia barbarensis (D,E). AT-Apical tuft, F-foot, 0-operculum, S-shell, Vc-Velar cilia, VP-Velum primordium

i 0,_ en > 0

u

0,_ > en

w

E E

0

() LL 0 en > () en

c

en

<( ------·----········---·-··-· 38

.Plate 5: Veligers of Simnia aequalis (A,B) and of Simnia barbarensis (C,D). Dg-Digestive gland, F-foot, M-mouth, 0-operculum, S-shell, St-statocyst, V-velum A ,. , 8

~,-~~~ F-~,..,.~~

c ~ //-:, D

v v 0 M St F F 0

Dg s s 40

Plate 6: Veligers of Simnia barbarensis (A-D) and of Simnia aequalis (E-H). All photomicrographs of veligers were taken at 50.4 X. Dg-Digestive gland, F-foot, M-mouth, 0-operculum, S-shell, St-statocyst, V-velum A

v v s 0 St

8 F

,.. . -v ·~ ·t _, .. ~. .. S t F · ~~ · . .., .' s

c G

D H

St

Dg 42

Plate 7: Empty egg capsules (EEC) and exit hole (Ex) of Simnia barbarensis.

--~-~-~-_ ---=-=-c--~-·=-c--;:::::::-·---_ ~-1

44 I

Plate 8: View showing granular shell sculpturing on the veliger shell of Simnia barbarensis (420X) (A), and of Simnia aequalis (450X) (B).

46

Plate 9: View showing shell edge on the veliger shell of Simnia barbarensis (430X) (A), and of Simnia aequalis ( 480X) (B).

48

Plate 10: View showing shell lip and ridge along columellar base on the veliger shell of Simnia barbarensis (400X) (A), and of Simnia aequalis (470X) (B).

tn 0

Plate 11: View showing shell surface of adult Simnia aequalis.

-----~----· . •·'-"--'--·-'·-' .. ., '~~·-'¥~""'-'~~--·=···'--"~~-~----=~~-~~ -

trl N

Plate 12: View showing mantle projections on adult Simnia aequalis and gorgonian polyps on Lophogorgia rigida.

-····~·------~---~-~--~·

U1 .j:>.

Plate 13: View showing ventral surface of adult Simnia aequalis.

·------..-~ •'• •: ~~·"·"'' • '"• "•>>_>""'-'"''"''""'="'="·~·"'"-·''~~M--··.'<~»•

Ul 0\

Plate 14: Adult female of Simnia barbarensis showing contents of mantle cavity. Ct-ctenidium, Dg-Digestive gland, Ge-Genital opening, Go-gonad, Hy-hypobranchial gland, Ma-Mantle edge, Os-Osphradium, Re-Rectum, Si-Siphon (/) u 0 (f)

., '

-,. ·· ~ : ..'· · .. .

~ . . .. . ~ ~ . ·· ~ .. .. ~.. " ~ :.. · ~ ·;··~ : ·. ~ · J V1 ()0

Plate 15: Adult male of Simnia barbarensis showing contents of mantle cavity. An-N1us, Ct-Ctenidium, Dg-Digestive gland, Go-Gonad, Hy-Hypobranchial gland, Ma-Mantle edge, Os-Osphradium, Pe-Penis, Si-Siphon

. ---·-····~-· ·-·-···--·~-- ~-"""~~-~~-----~~----· _.., _____ ----- 0 c Ol (!} <{ 0 Cl. 0\ 0

Plate 16: View of adult Simnia barbarensis on the sea pen Acanthoptilum gracile.

62 - 64

Plate 18: Transverse row of teeth from the radula of Simnia barbarensis (A)--(a) median tooth with 7 X 2 small cusps (b) lateral tooth (c) two marginals. Median tooth of Simnia aequalis with 5 X 2 small cusps (B). A

c c b b

B (j\ (j\

Plate 19: View of Simnia barbarensis feeding on the sea pen Acanthoptilum gracile.