California Musssel Shell, Mytilus californianus

California Mussel Shells, Mytilus californianus. Shell collected off the beaches of Southern California, May 2014. Size:  10.9 cm (4.3 inches) x 6.5 cm (2.6 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

The California Mussel, Mytilus californianus (Conrad, 1837), is a is a bivalve mollusk that is a member of the Mussels of the Mytilidae Family. The shell is large and elongated with a straight anterior margin and a curved posterior margin. The mature shells have a bluish-black color; the juveniles can have brown or white streaks. The California Mussel Shell reach a maximum length of 25 cm (9.8 inches) and 14 cm (5.4 inches) in height.

The California Mussels attach themselves to surf washed rocks and pier pilings and are found at depths up to 90 m (295 feet). Their presence is a good indicator of water quality as they require clean water for survival. They are filter feeders and filter phytoplankton and fine detritus from the water. In turn they are preyed upon by Ochre Starfish, Pisaster ochraeus. The California Mussels are edible and have been used for hundreds of years by local indigenous people as a food source.  They range from the Aleutian Islands to Cabo San Lucas, Baja California Sur and are also found around Socorro Island.

Synonyms include Mytilus californicus, Mytilus canalis, and Mytilus zonarius.