Two gnathiid isopods utilizing empty tubes of the polychaete worm <i>Spirobranchus akitsushima</i> in the Seto Inland Sea, western Japan, with the description of a new species

Two gnathiid species were collected from around Kagawa Prefecture, Seto Inland Sea, western Japan. One species was described as Caecognathia tubicola sp. nov. with detailed morphological examinations of male and female adults and larvae. A total of 130 individuals of C. tubicola were obtained from empty tubes of the polychaetous annelid Spirobranchus akitsushima in the intertidal zone. This species probably completes its life cycle around the aggregation of empty calcareous tubes of S. akitsushima on bedrock, as larvae at all developmental stages were found. Some adult females have significantly narrow thoraxes, a morphology that may be adapted to the elongate tubes. Small numbers of Elaphognathia cornigera (Nunomura, 1992) were also found in empty S. akitsushima tubes.