There are 3 species of intertidal mussels on the west coast of North America.  The California mussel Mytilus californianus is present from Alaska to Baja California, Mexido; the bay mussel Mytilus trossulus is present from Alaska to Morro Bay, California; and the bay mussel Mytilus galloprovincialis, an introduced species from the Mediterranean, is present only in southern California south of Morro Bay. All species are edible, and Mytilus trossulus is commercially cultured in Puget Sound.  The California mussel M. californianus is equally tasty, but its orange-coloured flesh and large size probably discourage most would-be diners. 

NOTE  these 3 species plus the Atlantic Mytilus edulis comprise the entire world representation in the genus.  Koehn 1991 Aquaculture 94: 125.

NOTE  references to mussels in English literature date back more than a thousand years.  One of the earliest that makes some sort of sense is from the writings of Chaucer in the year 1374: “...as oystrys and musculis and other swiche shelle fyssh of the see”.  Written records of mussel culture apparently commence with a shipwrecked Irishman, Patrick Walton who, stranded and hungry on a desolate French shore in the year 1235, set out nets to capture seabirds for food and ended up growing mussels, which probably tasted better than the seabirds anyway, and founding the bouchet system of net culture still in practise today

NOTE  analysis of over 11,000 shell remains at 28 middens on San Miguel Island, California shows that indigenous peoples continuously harvested mussels Mytilus californianus over 10,000yr of the Holocene Epoch.  Through that time the mean size of harvested mussels significantly declined from about 47mm length to about 39mm.  Erlandson et al. 2008 J Archaeological Sci 35: 2144; see also Braje et al. 2007 Am Antiquity 72 (4): 735 for similar information from the same research group for Santa Rosa Island

Phylum Mollusca (lit. “soft” or “shellfish” L.)

Class Bivalvia (lit. “2 folding doors” L.), referring to the 2 parts of a clam or scallop shell joined by a flexible hinge

SubClass Pteriomorpha (lit. “wing form” G.), including bivalves that attach by byssus threads or cementation

Order Mytiloida, containing mussels (Family Mytilidea)