Polytypic Mytilus edulis, with a name for the Baltic subspecies (Bivalvia: Mytilidae)

The four taxa of Mytilus represented in European waters are characterized morphologically, with references to distribution, nomenclature, and molecular data. The so-called Baltic M. trossulus is described as M. edulis balthicus subspec. nov. Only two Mytilus species are accepted in the area, viz. M. edulis, with M. e. edulis, M. e. galloprovincialis, and M. e. balthicus subspec. nov., and M. trossulus. To stabilize the use of M. edulis, the type locality of that taxon is restricted to the North Sea off the Dutch coast.