Pinnixa sp. (Gaper pea crabs)
2005 Mary Jo Adams
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
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.