Molecular phylogenetic analyses were conducted to clarify how genetically homogeneous the common Japanese species of Marphysa known as Iwa-mushi is. This is a well-known polychaete used as a fishing bait that was first described as Marphysa iwamushi Izuka, 1907 (type locality: Japan and Taiwan) and later synonymized to Marphysa sanguinea (Montagu, 1813) (type locality: England). The nucleotide sequences of a nuclear gene (18S rRNA) and two mitochondrial genes (16S rRNA and cytochrome c oxidase subunit I (COI)) were compared between specimens newly collected from 14 localities in Japan including commercially sold fishing baits and DDBJ/ENA/GenBank data for congeneric species. Our results show that the Japanese Iwa-mushi is not a single species but a species complex comprising five genetically well-separated clades that were tentatively designated as five undetermined species (Marphysa spp. A, B, C, D, and E). It is unclear whether any of these species corresponds to M. iwamushi. The COI nucleotide sequence of Marphysa sp. A was almost identical to that of M. victori Lavesque, Daffe, Bonifácio & Hutchings, 2017 (type locality: France) and M. bulla Liu, Hutchings & Kupriyanova, 2018 (type locality: China), suggesting that they are conspecific and supporting the hypothesis of Lavesque et al. (2017) that the population in France was introduced from Japan. The COI sequence of Marphysa sp. B corresponds to that of M. maxidenticulata Liu, Hutchings & Kupriyanova, 2018 (type locality: China). Marphysa sp. E was found only in Tokyo Bay and may be an alien species that was introduced by importing live fishing bait. Our results indicate that the European species M. sanguinea is not distributed in Japanese waters.

No abstract

No abstract

No abstract

Diplocirrus nicolaji is a flabelligerid worm originally described from shallow waters of Peter the Great Bay, Sea of Japan. Later, this species was also recorded from Japan, but detailed data were not provided; thus the occurrence of D. nicolaji in Japan needs to be confirmed based upon additional material. The collection of 20 D. nicolaji individuals from four localities along Japanese coasts (the Sea of Japan and western Pacific Ocean), allowed us to provide detailed morphological observations using stereoscopic and scanning electron microscopy. Partial cytochrome c oxidase subunit I sequences were obtained for phylogenetic analysis. Although the morphological analysis detected a few variations in palp length and body colour in ethanol among the local populations, the phylogenetic analysis confirmed their conspecificity with little genetic divergence. This is the first report of D. nicolaji from the western Pacific Ocean and extends its distribution southward.