Homalopoma emulum (Seguenza, 1876), a bathyal cold stenothermic gastropod in the Mediterranean Pleistocene

Homalopoma emulum (SEGUENZA, 1876) is a poorly known gastropod from the bathyal deposits of the Mediterranean Lower Pleistocene (Strait of Messina area). Its affinity with Homalopoma globuloides (DAUTZENBERG & FISCHER, 1896), living on the bathyal bottoms of the Northeast Atlantic Ocean (Azores and Gulf of Biscay), is very high and the two species are more closely related than two simply congeneric species. Homalopoma emulum belongs to a category of Mediterranean Plio-Pleistocene deep-water species characterized by remarkable taxonomic, morphologic and ecologic affinities with deep-water species from the Atlantic Ocean, or extra-Mediterranean areas in general. Such affinities seem to indicate a cold-stenothermic character, incompatible with the present deep homothermy in the Mediterranean Sea. The reason for the extinction of these species is referred to homothermic episodes which took place cyclically during the interglacial phases of the Upper Pleistocene. A progressive and selective extinction of these species led to the present lack of cold-stenothermic species in the Mediterranean deep benthos.