A revision of the “northern guest” Ostracoda (Crustacea) occurrence in the Quaternary of the Mediterranean area

In this paper the revision of the “northern guest” ostracods widespread in the Mediterranean area during Quaternary time is proposed. The abundant literature on this topic lists up to twenty-three species. They have been critically revised and a list of only twelve true “northern guests” is provided: Acanthocythereis dunelmensis (NORMAN, 1865), Bythocythere turgida SARS, 1866, Bythocythere zetlandica ATHERSUCH, HORNE & WHITTAKER, 1983, Cythere lutea MÜLLER 1785, Cytheropteron depressum (BRADY & NORMAN, 1889), Cytheropteron punctatum BRADY, 1868, Cytheropteron testudo SARS, 1870, Hemicythere villosa (SARS, 1865), Paradoxostoma abbreviatum SARS, 1866, Paradoxostoma ensiforme BRADY, 1866, Paradoxostoma tenuissimum (NORMAN, 1869) and Semicytherura angulata (BRADY, 1868). These species are generally rare, being found with very few specimens and mainly in one locality. Only Cytheropteron testudo and Cytheropteron punctatum have been reported with a wide geographical distribution in Italy and in the Aegean Sea. The twelve “northern guest” ostracods entered the Mediterranean at different times, being more abundant in the Early Pleistocene Sicilian substage. Only one study on the Last Glacial Maximum marine ostracods has been carried out recording the presence of C. testudo. The record of loose valves of “cold” ostracod species (C. testudo, P. tenuissimum and B. turgida) among the living Mediterranean assemblages suggests that they could have migrated into the Mediterranean even during Late Pleistocene time. In this paper, a critical revision of the existing literature about “northern guest” ostracods is presented, together with their stratigraphical and geographical distribution in the Mediterranean, and three new “northern guest” ostracod species are added.