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Pinnixa sp. (Gaper pea crabs)

photo of pea crabs
Copyright © 2005 Mary Jo Adams

 

Three species of pea crabs can be found living in the mantle cavity of the fat gaper clam ( Tresus capax ).   They are Pinnixa littoralis , Pinnixa faba , and Fabia subquadrata . (Pictured is Pinnixa sp.)   Pea crabs of various species inhabit or are associated with other bivalves, sea cucumbers, burrows of spoon worms and ghost shrimp, and the tubes of polychaete worms.   These pea crabs may exist as commensal species or as parasites.   In the gaper clam, the pea crabs are considered commensal.

 

Pea crabs are generally found in pairs within the clams.   (A clam may contain more than two pea crabs but only two are sexually mature.)   Of the two Pinnixa species in Puget Sound area gaper clams, Pinnixa faba is more common.   For both species, the female is larger, having a carapace width of up to 1 inch.   Carapace width for the male is about ¾ inch.   These two species of pea crabs are very similar in appearance.  

 

This page was created by Mary Jo Adams on 11/20/05.

 

 

photo of pea crab

photo of pea crab