Systematics of the Acanthocardia paucicostata group in the Mediterranean Plio-Pleistocene, with descriotion of a new species (Bivalvia, Cardiidae)

Three Acanthocardia species, namely A. paucicostata (Sowerby 1841), A. bianconiana (Cocconi 1873) and a new species herein described are particularly similar to each other, sharing some shell characters: shell relatively thin-walled, compared with the congeners, tending to be antero-posteriorly elongate, bearing a low number of radial ribs (15-18). A. paucicostata is an extant species with a stratigraphic distribution ranging back to the Late Miocene at least. A. bianconiana, regarded as a variety or subspecies of A. paucicostata in the past literature, had a Plio-Pleistocene Mediterranean distribution. The new species, A. brunettii n.sp., the smallest Acanthocardia species so far known and with an unusually elongate shape, also had a Plio-Pleistocene distribution. There are evidences that the paucicostata group also had representatives in the Miocene, either in the paleo-Mediterranean and the the Paratethys.