We examined specimens which have hitherto been identified as the operculate land snail Metalycaeus vinctus (Pilsbry, 1902) (formerly Chamalycaeus vinctus) in the National Museum of Nature and Science, Tsukuba, Japan. We found among these specimens another morphologically distinct taxon. Field investigation and examination of other newly-collected specimens confirmed that the real Metalycaeus vinctus lives in the northern part of Tanegashima Island, whereas the new species, Metalycaeus minatoi Páll-Gergely n. sp. mainly inhabits the southern part. The two species can be distinguished mainly by the morphology of the body whorl surface along the sutural tube: that of Metalycaeus minatoi n. sp. is more densely ribbed (26–41 ribs, mean: 33.0) and has lower ribs, which results in a nearly smooth shell surface whereas Metalycaeus vinctus (17–23 ribs, mean: 19.6) has elevated and sharp ribs. A third species, also reported from this island, Dicharax (?) tanegashimae (Pilsbry, 1902) was also found by us. The morphology of the penis, radula, operculum, and shell morphology of both Metalycaeus species, and penis morphology of D. tanegashimae are described and illustrated.
Two new species of the genus Calagrassor Kantor et al., 2013 are described. Calagrassor analogus n. sp. is distributed in Japan, the East China Sea and Taiwan, and has been previously confused with Aulacofusushiranoi (Shikama, 1962). Differences in protoconch morphology serve to distinguish C. analogus n. sp. from A. hiranoi and differences in sculpture serve to distinguish this new species from C. aldermenensis (Powell, 1971) and C. hayashii (Shikama, 1971). A second and hitherto unknown species is described from Japanese waters as Calagrassor hagai n. sp. Differences in spiral and axial sculpture serve to distinguish it from other known species in the genus.
The identity of Siphonochelus japonicus A. Adams, 1863 and S. nipponensis Keen & Campbell, 1964, both described from Japan, is discussed and updated. A neotype is here designated for S. japonicus. A new Siphonochelus species S. mozambicus is described from Mozambique and compared to the Japanese species, to S. arcuatus (Hinds, 1843) and S. pentaphasios (Barnard, 1959) both from South Africa, to S. rosadoi Houart, 1999 from Mozambique and to S. stillacandidus Houart, 1985 from Madagascar.
Assessments of genetic diversity, divergence and population structure of two species of threatened freshwater pearl mussels, based on allelic frequencies of 16 allozyme loci and partial mitochondrial 16S rRNA sequences (489 bps) were conducted for 17 populations of Margaritifera laevis and six populations of M. togakushiensis on Hokkaido and Honshu Islands, Japan. No evidence of hybridization was apparent between the two species. Genetic diversity within populations and divergence among populations were somewhat higher in M. laevis than in other threatened congeners. In contrast, M. togakushiensis showed allozyme monomorphism. Although the two species differed in 10 bp substitutions in the examined region of the 16S rRNA gene, no sequence variations were evident within both species. Genetic diversity within these two species was relatively low when compared with those of bisexual freshwater clams and marine mollusks.
The host species for glochidia of unionid mussels were examined in Lake Anenuma, Aomori Prefecture. As a result, Anemina arcaeformis was recorded for the first time from Aomori Prefecture and was found to infect two host fish species (Gymnogobius castaneus and Tribolodon hakonensis). Sinanodonta sp. was found to infect four species (Hypomesus nipponensis, G. castaneus, Tridentiger brevispinis and T. hakonensis); Hyriopsis schlegeli infects three species (H. nipponensis, G. castaneus and T. brevispinis), and Inversiunio jokohamensis also infects three species (G. castaneus T. brevispinis and T. hakonensis). The fish species composition was investigated and the prevalence of infection by unionid mussel glochidia for each host species in Lake Anenuma was investigated. Hypomesus nipponensis was the dominant fish species. Sinanodonta sp. mainly utilized H. nipponensis, A. arcaeformis utilized two species (G. castaneus and T. hakonensis), and the two other unionid species (H. schlegeli and I. jokohamensis) mainly utilized G. castaneus.
Mytilus trossulus Gould, 1850 is a mytilid bivalve with a boreal distribution in the northern Pacific Ocean, northern Atlantic Ocean, and Baltic Sea. The distribution of M. trossulus in Japanese waters was hitherto believed to be restricted to the northernmost island of Hokkaido. However, we discovered dry specimens and dead shells of this species on the northern and central Japan Sea coasts of Honshu Island. Specimens were collected before 1936, before 1948 and in 1951 from Shikaura, Fukui Prefecture (35°56´N, 135°59´E), and were archived at the Fukui City Museum of Natural History as "Mytilus edulis Linnaeus 1758". Dead shells with rotten soft bodies were collected from the Kisakata sandy shore, Akita Prefecture (39°12´24˝N, 139°53´40˝E) on March 29, 2014. In addition, we found old records of the nonindigenous congener M. galloprovincialis Lamarck, 1819 in molluscan lists that were published in Akita, Niigata, Ishikawa and Fukui Prefectures from the 1930s to 1950s. This species was introduced to Japan before 1932 and appears to have been infrequently confused with M. trossulus. In 2007, 2010 and 2014, we conducted field surveys in the regions where the dry specimens and dead shells had been collected but found no M. trossulus specimens. In view of the results of the field surveys and water temperature regime in its distribution range, we believe that the dry specimens and dead shells had drifted from the more northerly Japan Sea coasts of Russia or Hokkaido. The old records of M. galloprovincialis in the molluscan lists may indicate the actual occurrence of the nonindigenous species during the early years of its invasion in Japan.