Medium-sized Fusinus specimens taken by trawlers in the East China Sea off China are examined. A new species, Fusinus emmae n. sp., is described, and review of comparable species from the same area is given. The characters of the protoconch are examined, with refer-ence to previously published studies.
The abyssal nudibranch genus Bathydoris Bergh, 1884 is characterized by having very strong jaw-plates on both sides of the buccal mass and bearing independent clusters of gills (= branchial leaves) at the posterior end of the body. A new species Bathydoris japonensis, collected from the Japan Trench, is described and illustrated herein. Hitherto no species of this genus has been known from around Japan.
A molecular phylogeny based on sequence data from two mitochondrial genes (COI and 16S) is presented for the genus Neptunea, including the type species of all the three subgen-era. Our results support the previously recognized subdivision of Neptunea into three subgenera (Neptunea s.s., Barbitonia and Golikovia) based on the conchological and radular characters. The fossil record suggests that the divergence of the three subgenera occurred as early as the Late Oligocene to middle Miocene, and that the Atlantic N. antiqua diverged from western Pacific species well before the opening of the Bering Strait in the Pliocene. A new species, Neptunea mikawaensis, is described systematically.
Genetic differences between two forms (tall and short forms) of the pulmonate limpet Siphonaria japonica were examined using isozymes in order to reveal their identity. Three local samples from the tall form, two local samples from the short form, plus S. laciniosa and S. acmaeoides samples as outgroups were examined. Following the isozyme analysis, 26 loci within 17 enzymes were available commonly to the two forms. Allelic compositions between the two forms show extreme differences from each other, alleles completely or almost replacing each other at the 18 loci. The genetic distances (D values) calculated from the allelic frequencies of the samples indicated considerably high values both among the tall form samples (D = 0.0060–0.0126) and short form samples (D = 0.0181), inferring high genetic divergence in local populations. The difference in D values between the tall and short form samples were between 1.3882–1.5114, figures normally considered significant at the inter-generic level. This difference in values is considerably greater than that between the D values of the tall form samples and S. laciniosa, and the genetic divergence degree between the two forms is thus greater than that at the inter-specific level in the genus Siphonaria. The given results suggest that the tall and short forms of Siphonaria japonica are distinct species, and a taxonomic revision is required.
Phylogenetic analyses using mitochondrial DNA (Cox2-Cox1) and nuclear DNA (ITS1) were performed on a critically endangered freshwater pearl mussel, Hyriopsis schlegeli, endemic to Lake Biwa, Japan, and a closely related Chinese species H. cumingii, which was introduced to Japan approximately 30 years ago. Using samples of typical H. schlegeli and H. cumingii, clear genetic differences between the two species were recognized in both molecular markers. Surveys of the genetic compositions of freshwater pearl mussels showed evidences of hybridization between the two species in culture farms in Lakes Kasumigaura and Biwa. Given that pearl culture farms are not completely isolated from natural water systems in Lake Biwa, these findings suggest that native H. schlegeli might be threatened by hybridization with H. cumingii. The wild population in Lake Anenuma, Aomori Prefecture, Japan would be the only remaining ‘pure' population of H. schlegeli free from hybridization and therefore be very important for conservation, although it originated from escaped cultured mussels.
Some additional specimens of Archivesicashiretokensis (Uozumi) (Bivalvia: Vesicomyidae), whose original description was insufficient were collected from the upper Miocene Rusha Formation on the Shiretoko Peninsula, eastern Hokkaido, and the species is described here in detail. This is the only fossil record of Archivesica in Hokkaido and the entire Okhotsk Sea borderland. The late Miocene coincides with the appearance of Archivesica in Japan, and marks the onset of the development of the modern Japanese vesicomyid fauna.