Two new species of the eulimid genus Hemiliostraca Pilsbry, 1918 are described based on specimens recently collected and on some preserved in museum collections: Hemiliostraca fasciata n. sp. from Japan and H. ophiarachnicola n. sp. from Japan and Taiwan. Hemiliostraca fasciata n. sp. has hitherto been identified as Eulima vincta, Subularia vincta or H. vincta in literature and museum collections, but it differs from the syntypes of Leiostraca vincta A. Adams, 1863, which were newly examined for the present study, in possessing non-colored apical whorls, three lines on the body whorl in dorsal view, a slender aperture, a relatively larger body whorl, and a flattened columella. Hemiliostraca ophiarachnicola n. sp. has often been misidentified as H. distorta in museum collections, but it can be distinguished from latter species by a combination of characters, such as the more slender earlier whorls, three lines on the body whorl in ventral view, the non-convex teleoconch whorls, and the evenly protruding outer lip margin. Hemiliostraca ophiarachnicola n. sp. was found attached to the ophiuroid Ophiarachna incrassata by its proboscis, and is the second Hemiliostraca species described from ophiuroids.
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.
This paper is the first report of the freshwater mussel Margaritifera togakushiensis from northern Sakhalin. Species identification was performed based on shell characteristics. Twenty six dead shells and one live mussel were collected from the Dagi River in northern Sakhalin. One pair of the dead shells was regarded as M. togakushiensis, whereas all of the other specimens were Margaritifera laevis (Haas, 1910) [= Kurilinaia zatravkini (Bogatov, Prozorova & Starobogatov, 2003)]. The white-spotted char, which is the host of M. togakushiensis, lives abundantly in the Dagi River. All habitats of M. togakushiensis are located within the distribution area of the white-spotted char. Based on this relationship, it is possible that M. togakushiensis widely inhabits the northern part of the Russian Far East, as well as Sakhalin and Japan.
Swimming behaviour of juvenile Mactra chinensis was observed in the laboratory. Clams of 7–15 mm shell length swam by pedal flapping after launching from the bottom by leaping. The average swimming speed of 7–9 mm clams was 6.0 cm s-1 and that of 9–15 mm clams was 7.8 cm s-1. The average distance swum reached 17.4 cm. Larger individuals of 31–35 mm shell length class did not show swimming behaviour but they performed leaping. Swimming by pedal flapping extended the range of locomotive distance through the water column at least 4.1 times over that achieved by leaping. Therefore swimming is thought to be an adaptive behaviour to reduce the risk of predation and increase the chance to find a better place to burrow.