|Pacific Blue Mussel|
We already noted that three kinds of blue mussels are closely related. They are often hard to tell apart.
The California mussel, Mytilus californianus, is a more distant relative. It is restricted to the wave exposed coast where it thrives, reaching a size of up to 30 cm in length.
Mussels belong to the class Bivalvia which includes clams, scallops, cockles, rock jingles and even shipworms--which, incidentally, aren't worms at all.