My agency manages shellfish and my group works primarily with bivalves. There are no current west coast species in the Mollusc section of the symbol library.
The primary bay clam species are:
Basket cockle, Clinocardium nuttallii
Gaper or Horse clam, Tresus capax
Butter clam, Saxidomus gigantea
Native Littleneck, Protothaca staminea
I have attached photos of each species.