BULLETIN OF MARINE SCIENCE, 50(1): 229-230. 1992

PINNOTHERES STROMBI (BRACHYURA: PINNOTHERIDAE) INFECTION IN A POPULATION OF STROMBUS PUGILIS (MESOGASTROPODA: STROMBIDAE)

Shawna E. Reed

The crab, Pinnotheres strombi. was first described from a single female specimen taken from the mantle cavity of a living West Indian fighting conch, Strombus pugilis. and reported to be commensal (Rathbun, 1905). The Pinnotheridae live as commensals or parasites in the mantle cavities of various bivalve mollusks, ascidians, echinoids, and in worm tubes (Williams, 1984). Generally, females remain in their respective hosts while the males are usually free-living. For ex- ample, p, ostreum females have soft exoskeletons as they remain for their entire lives in their host oyster whereas the males have normal chitinization (Barnes, 1980). During May 1990, nine female P. strombi were collected from the mantle cavities of living S. pugilis. These conch were collected from a colony located around a freshwater pipeline running from Isla Magueyes to Mata La Gata reef, off the coast of La Parguera, Puerto Rico, at a depth of9 m. A total of 125 conch were examined (incidence of crab infection: 7.2%); only female crabs were found, one per conch. There appeared to be no preference for sex of the conch. The crabs were found on the upper portion of the gill of the conch. This area of the gill appeared necrotic under light microscopic study; however, infected conchs be- haved normally and appeared to be otherwise unaffected. Two other populations of fighting conch that have also been heavily sampled have not yielded any crabs. Both of these populations are located downcurrent of the infected population; however, there are intervening reefs, and a surface distance of 1.5 km to the closest known population, and 3 km to the second colony. The former inhabits the same bottom type at an equal depth whereas the latter population is found in an enclosed mangrove bay (maximum depth: 4 m). Eight of the nine female crabs collected were gravid. Two of these females were placed in an aerated aquarium where the eggs hatched. The larvae were successfully raised to the megalopa stage on a diet of Isochrysis sp. and Artemia nauplii within 10 days of hatching at an average water temperature of 24°C (field temperature averaged 29°C). One female became gravid again in the aquarium; however, both females died after 4 weeks, probably due to starvation. No males of this species of crab have yet been found although they may be free-living and smaller as they would have to enter the conch in order to mate with the females unless they copulate with the females as small crabs ('invasive stage') and then die as reported for P. ostreum (Hartnoll, 1969). Female crabs placed in an aquarium with new hosts were unable to enter the conch as it reacted violently to the crab attempting to crawl into the mantle cavity, and was able to brush the crab off. Most likely, females enter the host as larvae or as small crabs, and settle in the mantle cavity where they grow to adulthood. A second sample of 100 conch collected in June 1990 from this same population failed to yield crabs; however, a third sample of 15 conch collected in January 1991 turned up one ovigerous female crab. The presence of this single female in a host conch shows that these crabs are capable of surviving the extended winter burial behaviour of these conch probably because they feed on the copious amounts 229 230 BULLETINOFMARINESCIENCE,VOL.50,NO.I, 1992 of mucus produced in the mantle cavity of the conch as does P. maculatus which infects mussels (Caine, 1975).

ACKNOWLEDGMENTS

I am indebted to Prof. C. E. Cutress for his identification of this species of crab. I would also like to thank G. Lopez who first showed me this colony of conchs, and to dive partner A. McGehee for review of the manuscript.

LITERATURE CITED

Barnes, R. D. 1980. Invertebrate zoology, 4'· ed. Saunders College/Holt, Rinehart, Winston, Phil- adelphia. 1089 pp. Caine, E. A. 1975. Feeding of Pinnotheres macu/atus Say (Brachyura: Pinnotheridae). Forma et functio 8: 395-403. Hartnoll, R. G. 1969. Mating in the Brachyura. Crustacean a 16: 161-181. Rathbun, M. J. 1905. Description of a new species of commensal crab. ProC. Acad. Nat. Sci. Philadelphia. 371-372. Williams, A. B. 1984. Shrimps, lobsters, and crabs ofthe Atlantic Coast of the eastern United States, Maine to Horida. Smithsonian Institution Press, Washington, D.C. 550 pp.

DATEACCEPTED: August 13, 1991.

ADDRESS: Department of Marine Sciences. University of Puerto Rico, Box 908, Lajas, Puerto Rico 00667.