Species of the genus Idas Jeffreys, 1876 (Mollusca, Bivalvia, Mytilidae), associated with sunken organic substrates in the Mediterranean Sea and the North-East Atlantic Ocean, are reviewed. A new species associated with old sunken whale bones “Idas” cylindricus n. sp., provisionally included in the genus Idas s.l., is described from the Gulf of Lion (western Mediterranean Sea). It is compared with Idas (s.l.) simpsoni (Marshall, 1900), the closest species and to other related species of the North-East Atlantic and Mediterranean Sea. The new species is characterised by a large size for the genus, inflated shape and rectangular outline, thick and brown internal ligament and the markedly anterior position of the umbo.
Mollusca, Bivalvia, Mytilidae, Bathymodiolinae, Idas, Mediterranean Sea, new species.