Exploring the diversity of the deep sea-four new species of the amphipod genus Oedicerina described using morphological and molecular methods

Collections of the amphipod genus Oedicerina were obtained during six expeditions devoted to the study of deep-sea environments of the Pacific Ocean. The material revealed four species new to science. Two species (Oedicerina henricisp. nov. and Oedicerina teresae sp. nov.) were found at abyssal depths of the central eastern Pacific in the Clarion-Clipperton Zone; one species (Oedicerina claudei sp. nov.) was recovered in the Sea of Okhotsk (north-west Pacific), and one (Oedicerina lesci sp. nov.) in the abyss adjacent to the Kuril-Kamchatka Trench (KKT). The four new species differ from each other and known species by the shapes of the rostrum, coxae 1 and 4, basis of pereopod 7, armatures of pereonite 7, pleonites and urosomites. An identification key for all known species is provided. The study of the cytochrome c oxidase subunit I gene of the four new species and Oedicerina ingolfi collected in the North Atlantic confirmed their genetic distinction. However, small intraspecific variation within each of the studied species was observed. In the case of the new species occurring across the KKT, the same haplotype was found on both sides of the trench, providing evidence that the trench does not constitute an insurmountable barrier for population connectivity. None of the species have so far been found on both sides of the Pacific.