First record of the family Caprellidae (Amphipoda: Senticaudata) from the abyssal zone of the Bering Sea with description of a new species of Cercops

Three species of the amphipod family Caprellidae were collected in the area of the submarine Piip Volcano, the northwestern Bering Sea, during 75-th and 82-nd research cruises aboard the R/V Akademik M.A. Lavrentyev in 2016 and 2018 using the ROV Comanche-18. Two morphospecies of the genus Caprella (Caprellinae) were found on the Northern Summit of the Piip Volcano (depth 373 m) and on its northern slope (749–986 m). A new species, Cercops caecus Kireev and Golovan sp. nov. (Paracercopinae), was sampled in the abyssal zone adjacent to its southern slope (3362 m), where it was found on hydroids growing on a hexactinellid sponge. The new species differs from all other species of the genus by the lack of eyes and the presence of two pairs of gills in contrast to three paired gills found in the other congeners. This is the first record of an abyssal species of the subfamily Paracercopinae, whose other representatives are known from the shelf and the upper bathyal zones of the North Pacific, Arctic, and North Atlantic. This finding demonstrates the parallel processes of colonization of deep-sea habitats occurring in different subfamilies of Caprellidae. An updated diagnosis and a key to the Cercops species are provided. For the first time for Paracercopinae, data on the molecular marker (18S rRNA) was obtained.