MOLLUSKS all have soft bodies surrounded by a hard shell. They include the bivalves, which have two hinged shells, like clams; the gastropods or snails, with a single shell that is often coiled in a spiral; and polyplacophores or chiton, whose shells are made up of a number of small overlapping plates.
Blue mussel 
Mytilus trossulus
Bivalve with thin, smooth blue or brown oval shell
Attached to rocks or pilings by a “beard” (byssus)
Edible and prized for its delicate flavor
Fast-growing filter feeder
Rock scallop 
Crassidoma gigantea
Round, flat, greenish to brown bivalve
Shell heavily encrusted with other animals
Orange flesh with tiny blue eyes
Large (often up to 10 inches wide)
Lined chiton 
Tonicella lineata
Leathery flat oval chiton
Where exposed, shell has fine zigzag lines
Shell color varies: greenish, pink, brown
Relatively small (up to 3 inches)
Friday Harbor Marine Health Observatory 