Pseudodiaptomus japonicus Kikuchi, 1928 (Copepoda, Pseudodiaptomidae), a brackish-water copepod formerly known as P. inopinus Burckhardt, 1913, on Sakhalin Island (Russian Far East)

Abstract

Abstract We determined the taxonomic status of Pseudodiaptomus inopinus on Sakhalin using specimens from different localities, because it is currently known as a complex of species. The specimens examined appeared to belong to P. japonicus, based on the structure of the female genital operculum. However, a few females lacked spinules on the medial surface of the first exopodal segment of the female P5, which has been described as a character distinguishing P. japonicus from its two sibling species. The species is distributed in brackish waters from the very south to the very north of Sakhalin Island. The northernmost locality on Sakhalin is also the northernmost record of the species.