First Record of the Siberian Diaptomus Leptodiaptomus cf. angustilobus (Copepoda: Calanoida) in Europe

A Siberian diaptomus, identified as Leptodiaptomus cf. angustilobus (Sars G.O., 1898), has been found for the first time in Europe (Russia, Nizhny Novgorod oblast, mouth area of the Kerzhenets River (Middle Volga), 56°6′5″ N, 44°57′28″ E). A brief morphological description with illustrations of the species is presented. Differences in the morphometry of abdominal somites, length of antennules, and size of the fifth pair of thoracic legs are shown between females from Nizhny Novgorod oblast and Siberia. We have also obtained data on the abundance of L. cf. angustilobus in the plankton community of the mouth area of the Kerzhenets River and described habitat conditions for the Diaptomidae species new to this region.