The genus Axinus Sowerby, 1821 in the Mediterranean basin (Bivalvia: Thyasiridae)

Deep-sea sampling in the lonian Sea and NW off Mallorca (Mediterranean) has provided articulated and isolated valves of Axinus grandis (Verrill & Smith, 1885), an extant North Atlantic deep-sea bivalve. Some earlier records from the Mediterranean Sea have been described under the name Halicardia ferruginea Di Geronimo, 1974. H. ferruginea as well as Mytilimeria fischeri Locard, 1898 and Mytilimeria saharica Locard, 1898 are shown to be junior synonyms and are transferred from the family Verticordiidae to the family Thyasiridae. Our material is assigned to the Late Pliocene to Early Pleistocene based on the nannoplankton content of sediment infilling articulated shells. A study of the ontogenetic development of shell characters, feasible as investigated material includes specimens from different growth stages, shows a shift in the position of the ligament from internal in juveniles to partly external in adults. The genus Axinus Sowerby, 1821 is known stratigraphically from the Early Eocene until the Recent and geographically from the North Sea Basin, Atlantic, Mediterranean and Paratethys. Although little is known about the ecology of Axinus Sowerby, 1821, the examination of fossil as well as Recent occurrences suggests that Axinus is typically associated with deep-sea reducing, hydrogen sulphide-rich environments.