2026-08-25 北海道大学,東京大学,京都大学
日本近海から得られた3種のIlyarachna属ミズムシ類とその分布。
＜関連情報＞
- https://www.hokudai.ac.jp/news/2026/08/23jsps.html
- https://www.sciencedirect.com/science/article/abs/pii/S0967063726000725
日本海溝・千島海溝で異なる水深分布を示す3種のIlyarachna属ミズムシ類の報告と2新種の記載 Three Ilyarachna species (Isopoda: Asellota: Munnopsidae) showing different bathymetric distributions in Japan and Kuril-Kamchatka Trenches, with descriptions of two new species
Mizuki Ohta, Keiichi Kakui, Shigeaki Kojima, Michitaka Shimomura
Deep Sea Research Part I: Oceanographic Research Papers Available online: 19 June 2026
DOI:https://doi.org/10.1016/j.dsr.2026.104719
Highlights
- Three swimming asellote species of Ilyarachna reported from the NW Pacific.
- The three species were distributed in different depth zones along the two trenches.
- COI haplotypes of abyssal species suggest gene flow between land/seaward populations.
- They may have narrower depth ranges, while abyssal species may cross the trench axis.
Abstract
The munnopsid genus Ilyarachna G. O. Sars, 1869 is one of the “swimming asellotes” that have paddle-shaped natatory pereopods. It comprises 46 species, most of which exhibit narrow geographic but broad vertical distributions. In this study, we morphologically and molecularly investigated Ilyarachna isopods collected from depths of 2886–7288 m in the Japan and Kuril-Kamchatka Trenches. These specimens include three morphospecies: Ilyarachna cf. kussakini, Ilyarachna abyssalis sp. nov., and Ilyarachna hadalis sp. nov., the latter two of which have been described here as new species. Kimura 2-parameter (K2P) distances among cytochrome c oxidase subunit I (COI) sequences from the three species were 16.5–17.2% (I. cf. kussakini vs. I. abyssalis sp. nov.), 14.8–16.1% (I. cf. kussakini vs. I. hadalis sp. nov.), and 6.2–7.7% (I. abyssalis sp. nov. vs. I. hadalis sp. nov.), respectively, whereas intraspecific K2P distances were less than 4%. The species were collected at different depth zones (2886–3519 m; 4026–6131 m; and 5976–7285 m) around the two trenches, suggesting that, as with other swimming asellotes groups, the vertical distribution of Ilyarachna isopods is narrower than previously expected. In addition, we also found that I. abyssalis sp. nov. occurs on both landward and seaward slopes across the trench axis. The landward and seaward COI haplotypes did not form an exclusive group but nested in a single group. It suggests that the two populations on both slopes may not be genetically isolated and the species may cross the trench axis by swimming or drifting.
