Revision of the Vernalis-Robustus Group of the Genus Acanthocyclops (Cyclopinae, Cyclopoida, Copepoda) from Continental Water Bodies of the Palearctic with the Description of a New Species

A revision of representatives of the complex vernalis-robustus group of the genus Acanthocyclops, characterized by 17-segmented antennules and elongated caudal branches, was carried out for Palearctic water bodies. In total, about ten taxa of this group were described for this region, including the invasive American species Acanthocyclops americanus (Marsh, 1893). Following this revision, six taxa were recognized as valid, including one more species A. borutzkyi sp. n. from Sakhalin Island, described here as new to science. A. magistridussarti Stoch et Bruno, 2011 from groundwaters in Italy was synonymized with A. orientalis Borutzky, 1966, also inhabiting caves in Primorye of Russia and South Korea. A. trajani Mirabdullayev et Defaye, 2002 and A. einslei Mirabdullayev et Defaye, 2004 (described from France and Germany) were reduced to junior synonyms of A. americanus and A. robustus (G.O. Sars, 1863), respectively. The descriptions of all six valid taxa are given, and an identification key for all species of this group from the water bodies of the Palearctic is provided.