California Mussels

The California mussel, Mytilus californianus, is a large edible mussel, a marine bivalve mollusk in the family Mytilidae.
This species is native to the west coast of North America, occurring from northern Mexico to the Aleutian Islands of Alaska. California mussels are found clustered together, 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.
Wikipedia