Mytilus edulis.
Systematically, blue mussels consist of a group of (at least) three closely related taxa of mussels, known as the Mytilus edulis complex. Collectively they occupy both coasts of the North Atlantic (including the Mediterranean) and of the North Pacific in temperate to polar waters, as well as coasts of similar nature in the Southern Hemisphere. The distribution of the component taxa has been recently modified as a result of human activity (invasive species). The taxa can hybridise with each other, if present at the same locality.
And I "see" them, naïade and men reclining in the ocean soft waves...