Any one of many species of marine bivalve shells of the
   genus Mytilus, and related genera, of the family Mytidae. The common
   mussel (Mytilus edulis; see Illust. under Byssus), and the larger, or
   horse, mussel (Modiola modiolus), inhabiting the shores both of Europe
   and America, are edible. The former is extensively used as food in
   Europe.