Taxonomic Revision of Serratina capsoides (Lamarck, 1818) (Bivalvia: Tellinidae), an Endangered Species in Japan

Abstract

Serratina capsoides (Lamarck, 1818), an intertidal tellinid bivalve species widely distributed in the Indo-West Pacific, has been considered endangered in Kyushu, the main distribution area in mainland Japan. In this study, we taxonomically revised this species on the basis of molecular phylogenic and shell morphology analyses. Molecular analysis of mitochondrial cytochrome c oxidase 1 and nuclear 5.8S ribosomal RNA (rRNA) + internal transcribed spacer 2 + 28S rRNA genes showed that S. capsoides could be divided into 3 different genetic groups. Morphological examination of newly collected samples, museum collections, and type specimens also recognized 3 morphological groups, which corresponded to those recognized in the molecular analysis. These 3 groups were referred to as S. capsoides (Lamarck, 1818), S. diaphana (Deshayes, 1855), and S. pristis (Lamarck, 1818). The results of this study indicated that the populations of S. capsoides in mainland Japan are actually those of S. diaphana, whose distribution is very limited and which is at a comparably higher risk of extinction than previously thought. More data about the distribution and genetic diversity of S. diaphana are required to establish a protection program for the species.