Pea Crabs in Clams and Cockles


Category 2 (In Canada and of Regional Concern)

Common, generally accepted names of the organism or disease agent

Oyster crab, Pea crab.

Scientific name or taxonomic affiliation

Pinnotheres pisum, Pinnotheres pholadis, Tumidotheres (=Pinnotheres) maculatus, Pinnixa faba, Pinnixa littoralis, Fabia subquadrata (Decapoda: Pinnotheridae)

Geographic distribution

Eastern and western USA, British Columbia, Canada.

Host species

Spisula solidissima, Mya arenaria, Macoma nasata, Venerupis (=Tapes) philippinarum, Protothaca staminea, Nuttalia obscurata, Panope generosa, Cardium norwegicum and other species (Hart, 1982) including oysters, mussels and scallops.

Impact on the host

The mantle cavity may contain several crabs thereby reducing market value. Numbers are limited by mantle space with no evidence of direct pathology. The crabs feed on food items collected by their hosts.

Diagnostic techniques

Gross Observations: Pea-crabs are visible to the naked eye within the mantle cavity, and measure 1 to 15 mm in diameter (mature females are the largest stage).

Methods of control

Precautions should be taken to prevent their introduction. Note: They can invade other commercially important bivalves such as Mytilus edulis, Placopecten magellanicus and Argopecten irradians.


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.

Marshall, W.L., S.M. Bower and G.R. Meyer. 2003. A comparison of the parasite and symbiont fauna of cohabiting native (Protothaca staminea) and introduced (Vennerupis philippinarum and Nuttalia obscurata) clams in British Columbia. Journal of Shellfish Research 22: 185-192.

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., McGladdery, (2004): Synopsis of Infectious Diseases and Parasites of Commercially Exploited Shellfish: Pea Crabs in Clams and Cockles.

Date last revised: May 2004
Comments to Susan Bower

Date modified: