A new species of the genus Leucothoe Leach, 1814 (Crustacea: Amphipoda: Leucothoidae) associated with a limid bivalve from Sugashima Island, Japan

A new species of leucothoid amphipod, Leucothoe limidicola sp. nov. was collected from the mantle cavity and tentacles of the file clam, Limaria hirasei (Limidae). Commensalism associated with bivalves has been relatively rare in the genus Leucothoe and the present new species represents the sixth species of bivalve-associated commensal in the genus. According to the molecular phylogenetic analyses based on the partial sequence of the 18S gene, this new species was recovered as sister to Leucothoe akaisen. There were ~1.5% and ~9.4% differences between these two species in the 18S and COI sequences, respectively, and seven species-specific indels in the former. Morphologically, the new species can be distinguished from Le. akaisen by the distally dentate lateral surface of male gnathopod 2 carpus and straight or weakly concave, oblique posterodistal margin of pereopods 6, 7 bases.