Abstract
To advance the limited understanding of the East Asian Elasmopus fauna, field surveys were conducted in Japan and South Korea. In the present study, a new species, E. lumbiniger sp. nov., 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, E. koreanus is recorded in Japan for the first time, and the known distribution range of E. mukuinu has been significantly extended. The nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I (COI) of these species were determined, and the genetic distances among Elasmopus species were provided. A key to the species of Elasmopus found in East Asia is also provided.