Intertidal Organisms EZ-ID GUIDES


on this species


Mytilus trossulus (Bay mussel)

photo of bay mussel
Copyright © 2005 Mary Jo Adams


This common mussel grows to about 4 ½ inches in length, has a smooth shell, and is black, blue-black, or brown in color.   Often found in large aggregations, it attaches itself to rocks, pilings, and other objects by means of byssal threads.   Look for this mussel along shorelines where the water is relatively calm.   Other common names for Mytilus trossulus are blue mussel, foolish mussel, and edible mussel.  


It is generally easy to distinguish this mussel from the California mussel ( Mytilus californianus ), which grows considerably larger, has coarse ribbing, and lives along the higher energy shorelines of the outer coast.


Two other mussel species have been introduced to the Puget Sound area that are not as easy to differentiate from Mytilus trossulus .   Those species are Mytilus edulis and Mytilus galloprovincialis .   In addition to having very similar appearances with each other and M. trossulus , they are believed to have hybridized making identification from external appearance a daunting challenge and creating considerable confusion.    




This page was created by Mary Jo Adams on 1/23/06.



photo of bay mussel