On the identity of Mytilus edulis forma giganteus Wood, 1874 (Pliocene, North Sea Basin), with implications for the generic assignment of other European Cainozoic mytilid bivalves

A Middle to Late Pliocene mussel from the southern North Sea Basin referred to previously as Mytilus edulis forma giganteus Wood, 1874, is here reassigned to the genus Perna Retzius, 1788. The name of the forma giganteus has proved to be a junior homonym; hence the species is here renamed P. woodi. It is characterised by, amongst other features, a near-exclusively aragonitic shell, in contrast to species of Mytilus, which have a predominantly calcitic shell. Almost all Cainozoic mussels from Europe generally placed in Mytilus should be reassigned to Perna. Similarities of these to the Pacific genus Crenomytilus Soot-Ryen, 1955, and the use of specific shell characteristics in the generic placement of mussels are discussed.