California Mussel, Mytilus californianus
The California Mussel, Mytilus californianus, is a large and edible mussel, a marine bivalve mollusk belonging to the family Mytilidae.
It is native to the west coast of North America, occurring from northern Mexico to the Aleutian Islands of Alaska. California mussels are found in clusters, often in very large aggregations, on rocks in the upper intertidal zone on the open coast, where they are exposed to the strong action of the surf.
The shell is thick and is often 80 to 130 millimeters in length, sometimes larger. It is blue on the outside with a heavy brown periostracum which is usually worn off except near the growing edge of the shell. The beaks of the shell are frequently eroded. The shell has coarse radial ribbing and irregular growth lines on the outer surface. The inner surface of the shell is blue and faintly pearly.
Similar to other mytilids, the animal is attached to the substrate with a very strong and elastic byssus.
This mussel prefers the high salinity, low sediment conditions found on open rocky coasts. However, they do not colonize bare rock easily, instead showing a preference for the shelter of pre-existing mussels and their biological filaments. They attach themselves to the hard surfaces using their thread-like byssus.
Given correct circumstances, California mussels can grow up to 8 inches in length and may live for more than twenty years.