Genetic Analysis of Pea Crabs of the Genus Pinnixa White, 1846 (Brachyura: Pinnotheridae: Pinnixinae) Illuminate Their Taxonomy within the Subfamily and a Phenomenon of Host Switching in One of the Most Abundant Species in Vostok Bay, Sea of Japan

Individuals of pea crabs, currently referred to the genus Pinnixa White, 1846 (Decapoda: Brachyura: Pinnotheridae), and identified as P. rathbuni Sakai, 1934, P. banzu Komai, Nishi and Taru, 2014, Pinnixa cf. eburna Wells, 1928, and P. tumida Stimpson, 1858 from the southern part of the Russian coast of the Sea of Japan, have been genetically studied for the first time. As molecular genetics data, including a multigene analysis (COI + H3 + 16S + 28S), has shown, that the pea crabs found in burrows of various marine invertebrates (polychaetes, enteropneustids, and burrowing callianassid shrimps) in Vostok Bay, Sea of Japan, identified as P. rathbuni, P. banzu, and P. cf. eburna, most likely belong to the same biological species. It has also been suggested that Scleroplax rathbuni (Sakai, 1934) comb. nov., a representative of the American genus Scleroplax, which has colonized the Asian coast of the North Pacific in the recent past, is now attempting to inhabit various potential hosts here which are currently free of associated symbiotic pea crabs. Other examples of similar host shifts are discussed in the article, including the case of the symbiotic polynoid polychaete Arctonoe vittata (Grube, 1855) (Annelida: Polychaeta: Polynoidae), which lives on gastropods, echinoderms, and other marine invertebrates in Vostok Bay, as well as also a few examples of related pea crab species have been found on different hosts worldwide.