A M. trossulus feeding while submerged. The mantle and body is visibile between the two valves. Its outer shell is used as a substrate for the acorn barncle, Balanus glandula.
Mytilus trossulus is a bivalve mussel common to North American Pacific shores.
It is found from mid-intertidal to subtidal waters. The mussel’s common names include bay mussel, edible mussel, blue mussel and foolish mussel. M. trossulus has only recently been differentiated from a similar mussel, M. edulis, found on Atlantic coasts. Electrophoretic work lead to the discovery that all natural populations of what was referred to as M. edulis on the North American Pacific coast are actually a distinct species and were subsequently renamed M. trossulus. Except for electrophoretic and distribution differences, the two species are indistinguishable.
M. trossulus has an elongated shell that is reaches about 10 cm in length. The outside of the shell is almost smooth and ranges in color from bluish black to brown. The shell is somewhat pointed at the anterior end and round on the posterior end. Unlike many other mussel species, M. trossulus has three small
teeth adjacent to the hinge. The animal is a continuous filter feeder when immersed in water.