A new species of Pseudodiaptomus (Copepoda: Calanoida) from Japan, with notes on the closely related P. inopinus Burckhardt, 1913 from Kyushu Island

摘要

A new species of the calanoid copepod, Pseudodiaptomus nansei sp. nov., which has formerly been identified as P. inopinus Burckhardt, 1913, is described from estuaries of the Nansei Islands, southernmost Japan. This new species was compared with a population of the closely related P. inopinus from the neighboring Kyushu Island, western Japan, which is redescribed here. The new species is readily distinguishable from P. inopinus by the absence of dorsal spiniform processes on the fifth pediger in bothsexes, short posterior projections of the genital operculum, and thin caudal setae of the female instead of swollen seta in P. inopinus. The mitochondrial gene cytochrome oxidase subunit I (mtCOI) sequences of P. nansei differed by 21-26% from the examined population of P. inopinus, in contrast to a 0-3% difference within the population of each species. The absence of descriptions identifiable to P. nansei in previous studies outside the Nansei Islands, coupled with no occurrence of P. inopinus there,suggests that P. nansei is endemic to Nansei Islands and geographically segregated from P. inopinus.