A new species of Janiralata Menzies, 1951 (Isopoda: Janiridae) from Japanese bathyal waters, with a review of the associations with invertebrates among the species of Janiralata

Abstract

Isopods of the genus Janiralata Menzies, 1951 (Asellota: Janiridae) are known from shallow and deep waters of the Northern Hemisphere. Most species are free-living, but some are symbiotic on the surface of other benthic invertebrates. We obtained from three beam- and four otter-trawl hauls 18 Janiralata asellote specimens from the bathyal zone off the Pacific coasts of Tohoku, northeastern Japan. Partial nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene (505 bp) were determined for 16 of the 18 collected specimens. Non-significant genetic differences (< 0.8%) indicated that the individuals were conspecifics. Morphological analysis indicated that all the specimens belonged to a single species, Janiralata plana sp. nov. based on the unique morphology of the anterolateral and distolateral projections on the head and pleotelson, surface and lateral margins of the body, antennula article 1, and of the male pleopod 1. Six of the 18 collected specimens were found attached to the surface of an unidentified sea anemone (Hormathiidae), ten to the solasterid starfish Crossaster borealis Fisher, 1906 and two were obtained from the bottom sediment. Three COI haplotypes of the new species were shared by individuals from two neighboring sites, which suggests that genetic isolation occurs on a relatively narrow horizontal scale, although the bathymetric distribution range was rather wide. We describe a case study of the geographic and bathymetric distributions of an asellote species with low dispersal ability and its genetically differentiated populations. Such approach could help elucidate the diversity and distribution of deep-sea organisms and their diversification processes.