Taxonomy of the genus Elasmopus (Crustacea, Amphipoda) in Japan and South Korea, with description of a new species

To advance the limited understanding of the East Asian <i>Elasmopus</i> fauna, field surveys were conducted in Japan and South Korea. In the present study, a new species, <i>E. lumbiniger</i> <b>sp. nov.</b>, is described. The new species is distinguished from its congeners by a strongly projected posteroventral corner of the epimeral plate 3, long slender setae on the anterodistal corner of the male gnathopod 2 carpus, a mid-palmar ridge on the male gnathopod 2 propodus, and a smooth posterior margin on the basis of pereopods 5-7. In addition, <i>E. koreanus</i> is recorded in Japan for the first time, and the known distribution range of <i>E. mukuinu</i> has been significantly extended. The nucleotide sequences of the mitochondrial cytochrome <i>c</i> oxidase subunit I (COI) of these species were determined, and the genetic distances among <i>Elasmopus</i> species were provided. A key to the species of <i>Elasmopus</i> found in East Asia is also provided.