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Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts

Pea Crabs in Geoduck Clams

Small commensal crabs (carapace about 2 mm x 3.5 mm) were occasionally observed within the mantle cavity or in the siphon channels of geoduck clams. They were white to transparent, with an orange/brown tint on the distal segments of the walking appendages and probably belonged to the family Pinnotheridae. There was never more than two crabs found in a clam, and crabs occurred in clams sampled from the west and east coast of Vancouver Island and from the central coast of British Columbia.

Pea crabs (Pinnotheres pisum, Pinnotheres pholadis, Tumidotheres (=Pinnotheres) maculatus, Pinnixa faba, Pinnixa littoralis, Fabia subquadrata (Decapoda: Pinnotheridae) ) have been reported from other species of clams (for example, Spisula solidissima, Mya arenaria, Macoma nasata, Venerupis (=Tapes) philippinarum, Protothaca staminea (Hart, 1982)) and other bivalves including oysters, mussels and scallops. In most cases, pea crabs have little impact on the health of their bivalve host. However, they probably feed on food items collected by their hosts. In some cases, the mantle cavity may contain several crabs thereby reducing market value. Usually, the numbers of pea crabs per each bivalve host are limited by mantle space.  There are no know methods of control. But, precautions should be taken to prevent their introduction. Because they tend not to be host specific, they can invade other commercially important bivalves.


Bower, S.M., J. Blackburn and G.R. Meyer. 1992. Parasite and symbiont fauna of Japanese littlenecks, Tapes philippinarum (Adams and Reeve, 1850) in British Columbia. Journal of Shellfish Research 11(1): 13-19.

Cheng, T.C. 1967. Marine molluscs as hosts for symbioses with a review of known parasites of commercially important species. In: F.S. Russell (ed.). Advances in Marine Biology. Volume 5. Academic Press Inc., London, p. 315-335.

Hart, J.F.L. 1982. Crabs and their relations of British Columbia. British Columbia Provincial Museum, Victoria. p. 234-237.

Moller Christensen, A. 1959. On the life-history and biology of Pinnotheres pisum. Proceedings 15th International Congress on Zoology (London 1958): 267-270.

Zmarzly, D.L. 1992. Taxonomic review of pea crabs in the genus Pinnixa (Decapoda: Brachyura: Pinotheridae) occurring on the California shelf, with descriptions of two new species. Journal of Crustacean Biology 12: 677-713.

Citation Information

Bower, S.M. and Blackbourn, J. (2003): Geoduck clam (Panopea generosa): Anatomy, Histology, Development, Pathology, Parasites and Symbionts: Pea Crabs in Geoduck Clams.

Date last revised: August 2020
Comments to: Susan Bower

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