STUDIES ON THE SYMBIONTS OF THE GORGONIAN , VIRGULATA (LAMARCK)

WENDELL K. PATrON Ohio Wesleyan University, Delaware, Ohio 43015

ABSTRACT Colonies of Leptogorgia in the vicinity of Beaufort, North Carolina, occur most commonly in shades of yellow or orange and harbor several of symbiotic whose adaptations are discussed. The snail Neosimnia uniplicata feeds on surface debris and material shed by the host and incorporates pigment from the host colony into its own shell. The gorgonian also harbors a small , Neopontonides beau/ortensis; a tissue-feeding , Tritonia wellsi; a bivalve, Pteria colymbus; and two unidentified species of copepods. The Balanus galeatus settles preferentially on the decaying egg masses of Neosimnia. It grows down to the axis of the gorgonian and, following the disappearance of the egg mass, is surrounded by host tissue.

INTRODUCTION The sea whip Leptogorgia virgulata (Lamarck) is a branching gorgonian or horny coral which grows to an overall length of about 60 centimeters and is quite common on hard, subtidal substrates in the vicinity of Beaufort, North Carolina. It harbors several quite specialized symbiotic animals. These are shown diagrammatically in Figure 1 and are the subject of this paper. A portion of this material has appeared in abstract (Patton, 1963).

MATERIALS AND METHODS A total of about 200 colonies of Leptogorgia were collected over a period of several years from various sites in the Beaufort area and examined for symbionts. The chief collecting site was the rock jetty on Radio Island, a locality inside Beaufort Inlet subject to fairly strong currents. Collections were made from 1 to 10 feet below mean low tide and were made primarily during the summer months. To reduce the loss of symbionts during col- lection, each colony was placed in a hand net, then freed from the substrate and brought to the surface. The symbionts were placed on pieces of Leptogorgia in dishes of sea water and observed under the microscope. Long-term experiments and observations were hampered by the fact that colonies of Leptogorgia kept in running sea water in the laboratory usually decomposed within a week, perhaps due to the large amount of sediment in the water. Survival was 420 Bulletin of Marine Science [22(2)

lem

FIGURE 1. Diagrammatic drawing of a colony of Leptogorgia and its symbionts: 1, Neosimnia uniplicata with mantle withdrawn; 2, N. uniplicata with mantle extended; 3, egg mass of N. uniplicata; 4, Pteria colymbus; 5, Neopontonides beaufortensis; 6, Tritonia wellsi; 7, Balanus galeatus. better in aerated tanks of artificial sea water. Brine shrimp nauplii were added to these tanks at regular intervals, and, although the polyps were never seen fully extended, specimens seemed to be in good condition for the first several weeks and survived up to 3 months. 1972] Patton: Animal Symbionts of Gorgonian Coral 421

THE HOST Leptogorgia virgulata, like other gorgonians, is a colonial organism and is composed of a central axis of protein and an outer layer of tissue known as coenenchyme. The polyps extend out of the coenenchyme into the water, but can be withdrawn, leaving a pattern of holes which are darker than the surrounding tissue. The polyps of L. virgulata are white and translucent and lack the symbiotic zooxanthellae found in many other species of gorgonians. In whole colonies in the field and in pieces of freshly collected Leptogorgia in laboratory dishes, the polyps tended to be expanded under reduced illumination and contracted under bright light, although this relationship was by no means absolute. Embedded within the coenenchyme are small, colored, calcareous spicules. The color of Leptogorgia varies from specimen to specimen, but, with only rare exceptions, is constant throughout the length of a given colony. In the Beaufort area, specimens of L. virgulata occur most com- monly in shades of yellow and orange, while red, purple, and white colonies are rare. In Chesapeake Bay to the north and at Alligator Harbor, Florida, in the Gulf of Mexico, purple colonies are common. The central axis is thin at the tip of a branch, becoming progressively heavier toward the base, and finally forming a plate of axial material which attaches to the substrate and enlarges as the specimen grows. The axis is normally covered by coenenchyme, but, particularly at the base of large colonies, may be exposed and thus available as a site for settlement by fouling organisms. Throughout the period when colonies of Leptogorgia were maintained in tanks of aerated water, thin sheets of spicule-containing material were seen to be shed by the gorgonian. This did not seem to be associated with decomposition and appeared to be a natural process. S. A. Wainwright and G. R. Murdoch (personal communication) have observed a similar phenomenon in the gorgonian Pterogorgia citrina. Under both field and laboratory conditions, this species sheds transparent, noncellular organic membranes that have spicules stuck to them and are fairly well covered with diatoms and other microorganisms.

THE SYMBIONTS Neosimnia uniplicata (Sowerby).-This is an elongate, thin-shelled, proso- branch gastropod and is the best known of the symbionts of Leptogorgia, having been reported by Osburn (1885) and several subsequent authors. It belongs to the Ovulidae, a fairly small family, all of whose members seem to live in association with cnidarians (Robertson, 1970). Several snails were usually found together on a host. In a related genus, Cyphoma, the occurrence of male-female pairs and intraspecific fighting behavior has been observed (Ghiselin & Wilson, 1966). This was not noticed in N. uniplicata. 422 Bulletin of Marine Science [22(2) With regard to feeding habits, specimens of Neosimnia are found moving up and down the branches of the colony with their oral area pressed against the surface. Occasionally an individual was seen to bite the tissue at the edge of the pore formed by a withdrawn polyp or to pull tissue from the exposed cut end of a branch. In the great majority of cases, however, there was no indication that living tissues were ingested, nor did microscopic examination of the gorgonian after a snail had passed reveal any sign of damage. However, both freshly collected and laboratory specimens of Neosimnia produce feces that contain gorgonian spicules. Although direct ingestion of living tissue of the host occasionally occurs, it is probable that material settling on the colony and the above-mentioned thin sheets of spicule-containing material shed by the host are major components of the diet. This would account for the presence of spicules in the feces and for the lack of damage to the host. When starved snails were placed on pieces of Leptogorgia that had been rubbed gently in carmine powder, the snails moved over the gorgonian and rapidly ingested the carmine and the host's mucus in which the carmine particles were entangled. N. uniplicata evidently has a more benign relationship with its host than do several other species of the family Ovulidae, which remove quite notice- able amounts of host tissue. Simnia spelta feeds on host coenenchyme and may denude portions of branches of the gorgonian Eunicella stricta (Theodor, 1967). A photograph (Berrill, 1966) shows two individuals of Cyphoma removing the coenenchyme from a specimen of Pseudopterogorgia and ex- posing the central axis. Simnia patula eats the flesh of the alcyonarian Alcyonium digitatum (Lebour, 1932), including contracted polyps (Fret- ter&Graham, 1962). R. Robertson (personal communication) has noticed scars on an alcyonarian caused by Calpurnus verrucosus. Females of N. uniplicata deposit gelatinous masses containing a variable number of egg capsules around the branches of Leptogorgia (Fig. 1). The hundreds of eggs in each mass are initially white, but become darker as de- velopment proceeds and hatch as brown-shelled veligers. The gelatinous mass remains in place for some time after hatching occurs and serves as a site for the attachment of and other organisms. Eventually, however, the mass breaks apart and drops off the branch. The host coenenchyme underneath the egg mass occasionally disintegrates, exposing the axis. It is much more common, however, for the tissue to be somewhat contracted but still appear healthy. This is quite unlike the situation in the gorgonian Eunicella stricta, where the egg masses of Simnia spelta usually cause necrosis of the underlying tissue. This exposes the central axis to settlement by fouling organisms. In some cases these organisms can withstand being overgrown and enclosed by the regenerating coenenchyme (Theodor, 1964, 1967). 1972] Patton: Animal Symbionts of Gorgonian Coral 423

TABLE 1

DISTRIBUTION OF SHELL LENGTH IN Two COLLECTIONS OF Neosimnia uniplicata

Number of specimens Shell length (mm) June 6-7, 1961 August 16, 1961

3.0- 4.9 1 5.0- 6.9 5 7.0- 8.9 13 9.0-10.9 12 11.0-12.9 6 11 13.0-14.9 16 7 15.0-16.9 21 2 17.0-18.9 6 1 19.0-20.9 5

Since Leptogorgia was not collected during the winter months, the exact period of egg-laying by Neosimnia is not known. A single egg-containing mass was found in the earliest collection, March 29, and in the latest one, November 13. In early June, egg masses of all stages from freshly deposited to completely spent are common, but young snails are not yet found (Table 1). As the summer progresses, young snails become common, and the largest specimens evidently die off (Table 1). In studying the develop- ment of Simnia spelta, Thiriot-Qui6vreux (1967) found that larval life lasted 2 to 3 months, a timespan which seems plausible for Neosimnia uniplieata. Osburn (1885), Field (1949) and Perry & Schwengel (1955) have all noted that the color of the shells of N. uniplieata is generally the same as that of the gorgonian colony from which they are collected. Similar cor- respondence between color of shell and color of gorgonian host has been found in Simnia spelta by Theodor (1967) and in Neosimnia acieu/aris by Robertson (personal communication). In the present study, the cor- relation between color of Leptogorgia and shell color of Neosimnia was by no means absolute. It was best for the yellow gorgonians, whose snails were generally bright yellow. The darkest orange shells were found on the darkest orange hosts, while the gorgonians of intermediate shades contained snails of a variety of shades other than bright yellow. In order to test whether the color of the snails is determined genetically or by the color of the host, young specimens of Neosimnia were collected in mid-September and maintained in aerated artificial sea water on gorgonians of a different color from those on which they were collected. Within 2 weeks, new shell of the color of the new host was clearly visible, and after 3 months there was a wide band of this color along the outer 424 Bulletin 0/ Marine Science [22(2)

FIGURE 2. Young specimen of Neosimnia coIlected from a yellow Leptogorgia and then kept for 3 months on an orange host. margin of the shell (Fig. 2). Neosimnia evidently obtains pigment from ingested spicules or tissue and transfers it to the shell being deposited. Early efforts to demonstrate change in shell color with change of host were unsuccessful, probably because midsummer snails were employed. These snails are commonly mature and have a thickened, light-colored lip along the outer margin of the shell and thus are not depositing clearly visible new shell material. The shell of Neosimnia is much thinner than is usual among prosobranchs. Although some or much of the protective function of the shell has been relinquished, the thin shell confers two decided advantages. It can adopt the color of the host without requiring a large amount of host pigment and secondly, there is a smaller proportion of dead weight to be held in place on the gorgonian. Since Leptogorgia lives in areas of fairly strong current flow, the latter factor is undoubtedly important. In the gastropod Thais lapillus, a thin-shelled form is found on exposed shores, while a thicker-shelled form occurs in more sheltered waters (Kitching et al., 1966). The incorporation of host pigment into the shell is not universal in the Ovulidae. In a study on the pigment of the purple stylasterine coral Allopora californica, Fox & Wilkie (1970) found that the shell of the symbiotic ovulid Pedicularia cali/arnica did not contain the carotenoid 1972] Patton: Animal Symbionts of Gorgonian Coral 425 pigment of the host. The purple color of the top whorl of the snail's shell is thus not derived directly from the coral and is presumably manufactured by the snail. In addition to a shell whose color corresponds generally with that of the host, the exposed soft parts of N. uniplicata also serve to render the animal inconspicuous. The translucent mantle can extend out over the shell and has small white projections (Fig. 1) which bear a resemblance to host polyps. The mantle tissue around these projections bears a lacelike pattern of dark markings, which further breaks up the outline of the animal and also creates a resemblance to the colored and dark areas seen on a colony whose polyps are withdrawn. Similar markings are seen on the mantle of Simnia spelta (Theodor, 1967). In Neosimnia, the foot bears a series of parallel lines extending radially outward. These are the same color as the markings on the mantle. The head, the siphon, and the proximal por- tion of the mantle have a uniform color which approximates that of mark- ings of the foot and mantle. There is a relation between the color of these tissue markings and the color of the host. A rare purple colony of Lepto- gorgia harbored a snail with strong purple markings on the body. Snails found on orange gorgonians had reddish brown markings, while yellow snails taken from yellow hosts tended to have dark brown or black markings on the mantle and foot. Tritonia wellsi Marcus.-This species is a small (up to 10 mm in length) nudibranch gastropod, white with small dorsal projections that resemble polyps of Leptogorgia (Fig. 1). It was described recently (Marcus, 1961) and is not particularly common, although some specimens may have been overlooked due to their small size. Specimens placed in dishes with pieces of Leptogorgia actively ingested the host tissue exposed at the cut end. Although egg-laying was never observed, several gorgonians from which T. wellsi was collected contained egg masses that presumably belonged to this species. They encircled a branch, were about 5 mm long, and con- tained several parallel, zigzag rows of eggs. A related species, T. hombergi, inhabits the soft coral Alcyonium digitatum and has been studied in detail (Thompson, 1961, 1962). In this species, young individuals browse on the outer covering of the coral, while larger specimens are capable of biting off large pieces of host tissue and leaving noticeable scars. Interestingly, the host occurs in an orange and a white color form and only the latter is suitable as food for the nudibranch. Pteria colymbus (Roding).-Small specimens of the Atlantic wing oyster (under 20 mm in shell length) are commonly found attached by their byssal threads to various parts of living colonies of Leptogorgia from mid- summer through the fall months (Fig. 1). Presumably, as they grow larger they bend the colony and either die or change positions, since larger speci- 426 Bulletin of Marine Science [22(2) mens (over 35 mm long) are only found attached near the base of the colony where the central axis is thick enough to support the bivalve with- out being bent over. The attachment of the byssus weakens the underlying host coenenchyme and may expose the axis to settlement by fouling organisms. Copepods.-Occasionally, when pieces of Leptogorgia with extended polyps are examined under a dissecting microscope, tiny copepods of the family Lamippidae can be seen moving about within the polyps, disappear- ing inside the coenenchyme and appearing again in another polyp, two or three polyps down the line. Another type of copepod is sometimes seen moving over the surface. Balanus galeatus (Linnaeus).-This barnacle forms conspicuous bumps on the gorgonian colony and occurs either in clusters (Fig. 1) or as single individuals. It attaches to the central axis by the basis and occasionally by the carina, which may be short or prolonged into a point (Pilsbry, 1916). Except for the pedal opening, the barnacle is covered by coenenchyme (Fig. 1). B. galeatus belongs to a subgenus Conopea that is restricted to gorgonians and millepore (Pilsbry, 1916). Dead are fairly common and are completely overgrown by host tissue. In looking over spent, but still intact, egg masses of the snail Neosimnia, several instances were noticed where young barnacles were growing in the underlying coenenchyme. This suggested some relationship between the egg mass and the barnacle, and numerous egg masses were therefore ex- amined in detail. Several contained barnacle cyprids attached to the mass in between the egg capsules, others contained small barnacles attached to the surface, while in still others there were smaIl barnacles with plates extending down to the underlying gorgonian. These stages no doubt alI represent Balanus galeatus, since it would be unusual for the larvae of non- commensal barnacles to settle on such a soft substrate. This arrangement is of obvious benefit to B. galeatus. The egg mass provides a place for initial attachment that is not exposed to host defenses. The barnacle plates then grow down through the shrunken coenenchyme of the host and attach to the axis. By the time the egg mass disintegrates, the barnacle is weIl established and will eventually be surrounded by gorgonian tissue. Many of the egg masses contained more than one barnacle, permitting eventual cross-fertilization by the adults. Although no young barnacle stages were seen growing on the gorgonian surface or on exposed portions of the axis, it is of course possible that some larvae of B. galeatus may settle directly on their host. In any case, the establishment of the commensal barnacle is clearly facilitated by the presence of the egg masses of Neosimnia. This represents an interesting situation in which one symbiont benefits from the activities of another. 1972] Patton: Animal Symbionts of Gorgonian Coral 427 Neopontonides beaufortensis (Borradaile).-This small shrimp (up to 10 mm in length) belongs to the subfamily Pontoniinae of the family Palae- monidae, a group containing numerous species symbiotic with invertebrates. This species is usually found resting motionless, with the walking legs wrapped around a branch of Leptogorgia (Fig. 1). The propodus of each of these legs is somewhat bowed outward, which facilitates grasping the branch. When disturbed, however, the shrimp is capable of rapid move- ment. N. beaufortensis is a scavenger feeding mainly on material on the surface of the host. When starved specimens are placed on a piece of Leptogorgia, there is a flurry of activity by the appendages, and the stomach can be seen to fill rapidly with spicules, mucus, and other material from the surface of the colony. When specimens were placed on pieces of Leptogorgia that had been rubbed with carmine, they rapidly ate the carmine particles and mucus in which they were entangled. One specimen was seen to remove material from inside an extended polyp. The are not entirely de- pendent on the gorgonian for food, as individuals kept in laboratory tanks were occasionally seen to hook themselves to the host with their posterior walking legs and stretch out to feed on surrounding sediment. On a few occasions, specimens made brief excursions to feed on material growing on the side of the tank, before swimming back to the host. The appendages most frequently used in feeding are the slender, chelate, first pair of legs (first pereiopods), which moved back and forth between the host and the mouthparts. The chela does not bear teeth on the inner margins of the fingers, or any concentrations of setae. The tips of the fingers, however, bear a number of stout, inwardly directed spines which seem well adapted for gathering and holding small objects. As has been reported for other palaemonids, the first pair of legs are also used in clean- ing activities around the gills. The fourth pair of legs occasionally go to the mouthparts, and appeared to be used in feeding. The largest appendages are the second pair of legs. They only rarely go to the mouthparts, and were used mainly in aggressive behavior. They are thrust forward at an oncoming shrimp and are held outwards and pulled back in sideways jabs at a shrimp approaching from the rear. As noted by Borradaile (1920), the females of N. beaufortensis show remarkable protective coloration. They contain yellow and deep red pig- ments in chromatophores located in the ventral half of the main portion of the body. By differential expansion of these pigments, they can match any color of their host, from yellow, to orange, to purple. Freshly collected females match the color of their host, but in general gradually become clear under reduced light in the laboratory. Males have the same pigments, but far fewer chromatophores, and so are basically translucent. Males are also more active than females. 428 Bulletin of Marine Science [22(2)

DISCUSSION It may seem surprising that any animals at all are found on the surface of Leptogorgia, since colonies of the gorgonian offer relatively little shelter and are quite open to inspection by predators. Part of the answer certainly lies in the inconspicuous appearance of the symbionts. With the exception of the bivalve Pteria colymbus, all of the symbionts visually blend in with their host. There are also behavioral modifications such as that of the shrimp N. beaufortensis, which remains motionless for long periods. The fact that the host may be one of several alternate colors presents a problem for the symbionts of Leptogorgia. This has been overcome by different means or "evolutionary strategies" in four different species. Fe- males of the shrimp Neopontonides beaufortensis possess yellow and deep red pigments in chromatophores and can match the entire range of host colors except white. Male shrimp are basically translucent. In the snail Neosimnia uniplicata, host pigment is incorporated into the shell, and the mantle has small projections that resemble coral polyps and color markings which make the shell less conspicuous. The barnacle Balanus galeatus is both camouflaged and protected by the host tissue which grows up around it. The nudibranch Tritonia wellsi does not match the color of its host. However, it possesses a white coloration and dorsal projections which resemble coral polyps. It is small enough to be inconspicuous at all times and almost totally concealed when the host polyps are fully expanded. Gorgonian tissue is probably distasteful to fish, and this in itself may grant a degree of protection to the symbionts. Gorgonians are abundant and varied in the Caribbean, and yet Randall (1967) found gorgonians in the stomachs of only 11 of the 212 fish species examined. In one of these, gorgonian tissue amounted to 12.6 per cent of the total stomach contents, while it was less than 5 per cent in three, and less than 2 per cent in seven. If the tissue of Leptogorgia is unpalatable or even repellent to fish, then fish will do little random picking at its surface. Thus, despite their exposed posi- tion, the symbionts of Leptogorgia could be freed to a considerable degree from the chance encounters with predators to which free-living species are continually exposed. This type of protection will only be effective if the symbionts are inconspicuous and do not attract the attention of predators. This is, of course, the case. The association of Leptogorgia and its symbionts seems to be a stable one. The small nudibranch Tritonia wellsi and perhaps the copepods feed on host tissue, but there is no indication that they affect host survival. Of the larger species, Neopontonides beaufortensis picks up material from the surface of the host, from within the polyps, and from the adjacent sub- stratum, while Neosimnia uniplicata feeds chiefly on material shed by the host and on debris settling on the host's surface. The above two species 1972] Patton: Animal Symbionts of Gorgonian Coral 429 may be of some benefit to the host by assisting in the process of debris- removal. The bivalve Pteria colymbus and the barnacle Balanus galeatus are feeders. With the exception af the capepads, a given calany of Leptogorgia generally harbors only small numbers of symbionts (usually 0-5 and seldom more than 10 individuals per species). The number of symbiont individuals present seems far less than could be supported by the available food and space, and there is no evidence that the different species are competing with each ather in any important way.

ACKNOWLEDGMENTS I am grateful to the Duke University Marine Labaratary for the use af space, to' Dr. R. Rabertson for helpful camments an a draft of the manu- script, to' Dr. Ernst Marcus for identifying the nudibranch, and to' Rayna Patton for her help in many ways. This study was supported in part by a NSF pastdoctaral award through the Duke University Marine Laboratary.

SUMARIQ

ESTUDIO DE LOS ANIMALES SIMBI6TICOS QUE VIVEN EN EL CORAL GORGON.kEO, Leptogorgia virgulata (LAMARCK) La gargania Leptogorgia virgulata se presenta en substratas duros en la vecindad de Beaufart, North Caralina, y haspeda varias especies de arganismas simbi6ticas. El huesped se present a en fases de distintas calores, sienda los tanas de amarilla y naranja las mas camunes. El gaster6pada prosabranquio Neosimnia uniplicata raramente causa dana visible a las garganias y se cree que se alimenta en gran parte de material contenienda espiculas desprendidas de Leptogorgia y de material que se asienta en la calonia. Se mastr6 que pigmentos de las gorgonias eran incarporadas a las canchas de ejemplares en crecimienta y par tantO' las caracoles tienden a igualar el colar de su huesped. El manta puede extenderse sobre la superficie de las conchas y tiene proyecciones que parecen p6lipas y marcas de calares que hacen la cancha menas conspicua. El pequeno, incanspicuo nudibranquia Trilonia wellsi se alimenta de tejida coralino. Un escaramujo, Balanus galealus, se adhiere al eje central de la gorgonia y excepta en la abertura pedial, esta cubierta par cenenquima del huesped. Las escaramujas j6venes se asientan en las masas de huevas del caracal Neosimnia y crecen hacia abaja dentro de la gargonia sub- yacente. Hembras del camar6n Neoponlonides beauforlensis paseen pig- mentos amarilla y rojo ascura y pueden igualar el calar de su huesped. Las machos san trasl6cidas. Esta especie es un necr6faga general de desperdicias en la superficie de la colonia y, ocasionalmente, en el sedi- mento que 10' rodea. 430 Bulletin at Marine Science [22(2) LITERATURE CITED BERRILL, N. J. ] 966. The life of the ocean. McGraw-Hill, New York, 232 pp. BORRADAILE, L. A. ] 920. On a new commensal prawn. Ann. Mag. nat. Hist., Ser. 9, 5: 132-133. FIELD, LOUISE R. ]949. Sea anemones and corals of Beaufort, North Carolina. Bull. Duke Univ. mar. Stn, No.5, 39 pp. Fox, D. L. AND D. W. WILKIE 1970. Somatic and skeletally fixed carotenoids of the purple hydrocoral, Allopora californica. Compo Biochem. Physiol., 36: 49-60. FRETTER, V. AND A. GRAHAM 1962. British prosobranch molluscs, their functional anatomy and ecology. Ray Society, London, 745 pp. GHISELIN, M. T. AND B. R. WILSON ]966. On the anatomy, natural history, and reproduction of Cyphoma, a marine prosobranch gastropod. Bull. Mar. Sci., 16: 132-]41. KITCHING, J. A., L. MUNTZ, AND F. J. EBLING ]966. The ecology of Lough Ine. XV. The ecological significance of shell and body forms in N ucella. 1. Anim. Ecol., 35: 113-] 26. LEBOUR, M. V. 1932. The larval stages of Simnia patula. J. mar. bioI. Ass. U.K., 18: 107-] ]5. MARCUS, E. 1961. Opisthobranchia from North Carolina. J. Elisha Mitchell Scient. Soc., 77: 14]-]51. OSBURN, H. L. 1885. Mimicry in marine Mollusca. Science, 6: 9-10. PATTON, W. K. 1963. Animal associates of the gorgonian coral Leptogorgia virgulata at Beaufort, N. C. Am. Zoo\., 3: 522. PERRY, LOUISE M. AND JEANNE S. SCHWENGEL 1955. Marine shells of the western coast of Florida. Paleontological Re- search Institute, Ithaca, N. Y., 318 pp. PILSBRY, H. A. 1916. The sessile barnacles (Cirripedia) contained in the collections of the U. S. National Museum; including a monograph of the American species. Bull. U. S. natn. Mus., 93: 1-366. RANDALL, J. E. 1967. Food habits of reef fishes of the West Indies. Stud. trop. Oceanogr. Miami, No.5: 665-847. ROBERTSON, R. 1970. Review of the predators and parasites of stony corals, with special reference to symbiotic prosobranch gastropods. Pacif. Sci., 24: 43-54. THEODOR, J. 1964. Contribution a l\~tude des gorgones. II. Ecologie: La faune et la flore contenues dans des excroissances de I'axe d'Eunicelia stricta (sensu Rossi). Vie Milieu (Supp\.), 17: 157-163. 1967. Contribution a l'etude des gorgones. (VI): La denudation des 1972] Patton: Animal Symbionts of Gorgonian Coral 431 branches de gorgones par des mollusques predateurs. Vie Milieu, Ser. A,18: 73-78. THIRIOT-QUIEVREUX, C. 1967. Observations sur Ie developpement larvaire et postlarvaire de Simnia spelta Linne (Gasteropode Cypraeidae). Vie Milieu, Ser. A, 18: 143-151. THOMPSON, T. E. 1961. The structure and mode of functioning of the reproductive organs of Tritonia hombergi ( Opisthobranchia). Q. JI microsc. Sci., 102: 1-14. 1962. Studies on the ontogeny of Tritonia hombergi Cuvier (Gastropoda Opisthobranchia). Phil. Trans. R. Soc., Ser. B, 245: 171-218.