Revision of Sinanodonta Species (Bivalvia: Unionidae) Native to Japan with Description of Two New Species

Abstract

Genetic analyses have detected five distinct lineages of Sinanodonta, including two potentially cryptic species, native to Japan. For the formal description of two new species (S. plana n. sp. and S. kyushuensis n. sp.), their shell morphological diversity must be examined. The linear morphometric shell indices were analyzed by performing linear discriminant analysis of these species. Sinanodonta tumens exhibited distinct morphological features, with a roundly ovate and inflated shell, and S. plana n. sp. exhibited an elongated ovate and flat shell. Sinanodonta calipygos was distinguished from S. lauta and S. kyushuensis n. sp. by the standardized convexity index. Although marginal differences in shell shape were observed between S. lauta and S. kyushuensis n. sp., young shells displayed contrasting colors, with a brownish-green periostracum in S. lauta and a greenish-brown hue in S. kyushuensis n. sp. Our research adds to the information available for the genus Sinanodonta, and we describe two new Sinanodonta species.