Description of a New Littoral Mantis Shrimp Species of the Genus <i>Bigelowina</i> (Crustacea: Stomatopoda: Nannosquillidae) from Japan, With a Note on the Identity of a Congeneric Species from the Ryukyu Islands

Bigelowina phalangium (Fabricius, 1798) is the only representative of the genus Bigelowina Schotte and Manning, 1993 known from the Indo-West Pacific region. In Japanese waters, this species has been reported from the littoral environments of the Ryukyu Islands to Honshu Island. Our morphological and phylogenetic analyses of specimens of Bigelowina from Japan found two allopatric species, one from the Ryukyu Islands and another from Kyushu to Honshu Islands. The Ryukyuan species is morphologically closest to B. phalangium, with slight differences in the morphology of the raptorial claw and the color pattern of the telson. In contrast, another species from Kyushu to Honshu Islands is here described as a new species, B. komaii sp. nov. The field survey conducted in this study suggests that the host of two commensal mollusk species previously reported from the burrow of species of Bigelowina at Nakatsu, Kyushu Island, is B. komaii sp. nov., not B. phalangium. An identification key to species of Bigelowina is also provided.