Molluscs hitherto recorded from deep-sea vent/seep environments in Japan are reviewed and listed based on various literature published up to 2004. Compiled data on holotype depositories and type localities as well as detailed distribution records with geographic and depth ranges, and type of habitat (vents and/or seeps) are given for each of 74 recorded species (2 polyplacophorans, 30 bivalves and 42 gastropods). Comparison of faunas at various localities revealed the following characteristics: 1) The Japanese vent/seep fauna is typified by the highest diversity of Calyptogena in the world. 2) Bathymodiolus is the second most diversified large-sized bivalve in Japanese vents and seeps. 3) Conspecific populations of Calyptogena and Bathymodiolus have been proven to occur both in vents and in seeps, but most other molluscan taxa are obviously either vent-or seep-specific. 4) Two major groups of deep-sea bivalves, protobranchs and anomalodesmatans, are rare or totally absent, in contrast to non-vent/seep environments. 5) Vent/seep-endemic limpets are highly diversified. 6) Neomphalids and peltospirids (so-called 'hot vent taxa') are absent, except for a single species. 7) Among caenogastropods, small-sized provannids (Provanna) are dominant, rather than large-sized ones (Alviniconcha and Ifremeria). 8) Naticid predators have never been found in the Recent fauna, although fossil records suggest their presence in seeps in the geologic past. 9) Some species of neogastropod predators have been reported as temporal invaders from the ambient environment. 10) Two species of chitons from vents in the Okinawa Trough represent the only record of polyplacophorans from chemosynthetic communities in the world. 11) No aplacophorans, monoplacophorans, scaphopods or cephalopods have been collected at Japanese vent/seep sites.
A new margaritiferid species, Margaritifera togakushiensis, is described from the Sakasa River at Togakushi, Nagano Prefecture, Honshu and the Furebetsu River at Furano City, Hokkaido, Japan. The anterior margin of the shell is semicircular and the shape of the adductor muscle scar is acute auriform, versus semi-elliptical and round auriform in M. laevis. The host fish of the glochidia is also different: Salvelinus leucomaenis for M. togakushiensis and Onchorhynchus masou for M. laevis.
Two new species of the family Ovulidae are described from off the Kii Peninsula, from Kuchinoshima Island and the Oshima-Shin-Sone Bank, Japan. Primovula astra n. sp. is closely similar to Primovula oryza Omi & Clover, 2005 in overall morphology, but it can be distinguished by its non-beaked posterior extremity and different dorsal marking. Phenacovolva vitrea n. sp. is most similar to Phenacovolva tayloriana Azuma & Cate, 1971, but differs from it in forming short and callously rimmed terminals, and having less flared margin.
We examined specimens of the non-indigenous mytilid bivalve Mytilus galloprovincialis in the Furukawa Collection of the Fukui City Museum of Natural History. In total, 14 specimens in 4 lots were found and identified as M. galloprovincialis, all of which were collected in the 1930s and 1940s and donated by the physician Tamizo Furukawa. Two specimens collected at Hiroshima before 1934 represent the earliest collection that we know of among all the specimens of this species existing in Japan. Six specimens collected at Kanazawa, Kanagawa Prefecture in 1937, and two specimens from Obama, Fukui Prefecture before 1948 were regarded as the earliest collections that we know of among the specimens collected in Tokyo Bay and the Japan Sea, respectively. The initial invasion history and range extension of this species into the Seto Inland Sea, Tokyo Bay and the Japan Sea is discussed, focusing on the first record in each sea area.
Two freshwater snail species of the genus Semisulcospira, S. libertina (Gould) and S. reiniana (Brot), inhabit various areas in the Japanese Islands. It has been pointed out that these two species are indistinguishable by their adult shell morphology. In the present study, genetic and morphological variations of the adult shell of the two species were examined, and the genetic relationship between them was inferred through starch gel electrophoretic analysis. The individuals examined of 19 populations mainly in the areas of the central to eastern Japan were separated into two almost-isolated groups without natural random mating between them. The Mpi locus is fixed for the allele Mpi^A in one group (MpiAA type) and for the allele Mpi^B in the other group (MpiBB type) except a few heterozygous individuals. The MpiAA type individuals live throughout the central to northeastern areas and Okinawa island in Japan, while the MpiBB ones are distributed in the area west of the Kanto district. As to the morphological features of adult shells, 85 percent of the MpiAA type individuals have smooth shells with no ribs, and pronounced ribs are recognized on the shell of 53 percent of the MpiBB type individuals. Except for the rib feature, there is no appreciable difference in the adult shell morphology between the two groups. Considering these morphological features and previous taxonomical research, the MpiAA type and MpiBB type individuals are assignable to S. libertina and S. reiniana respectively. According to molecular phylogenetic tree based on the gene frequency at 12 gene loci, MpiBB type individuals are inferred to be derived from a population of MpiAA type individuals.
Intertidal molluscan communities were surveyed on six lava boulder shores on Sakurajima Island, Kagoshima Prefecture, which has a large active volcano. Each shore was thought to have different geological characteristics since they consist of lava extruded during four volcanic eruptions (A.D.1471-76, 1779, 1914, 1946). This study aims to show the relationship between the community structure of intertidal Mollusca and the characteristics of boulders on the shore as well as to compare the intertidal molluscan fauna of shores formed by different eruptions on Sakurajima Island. The survey was carried out between May and July 2001. The number of each species and the size of boulders in quadrats placed at regular intervals were recorded. Thirty species were found on the six shores and the density of all species showed more than ten-fold differences in the middle intertidal area between the shores with the highest and the lowest densities. Cluster analysis did not group molluscan communities in the shores with lava extruded during the same eruption because of variation within each shore. The result of multiple regression analysis showed that number of species increased with decreasing tidal level and increasing surface area of boulders per quadrat, and that the number of molluscan individuals increased with the mean volume of boulders.
Seasonal changes in the growth and abundance of Ittibittum parcum (Gastropoda: Cerithiidae) living on the brown alga Sargassum thunbergii were studied from January to December 2004 on the eastern coast of Sagami Bay, central Honshu, Japan. The density of individuals reached its maximum in April, and fell to a minimum in May. The plant reached its maximum length in May, and thereafter decreased to reach a minimum in November. These seasonal changes in plant length preceded changes in the abundance of I. parcum by one month. Newly settled juveniles of I. parcum appeared in July, and grew rapidly thereafter. The lifespan of the gastropods was estimated to be one year.
The availability of the Japanese eight-barbel loach Lefua echigonia as a host fish for the glochidia of the unionid mussel Pronodularia japanensis was investigated. The hosts to which the glochidia were attached in a paddy field ditch were cultured in tanks (61, 28±0.5℃) for nine days. Glochidia and juveniles that became detached from the hosts were counted daily. Juveniles appeared about six days after glochidia attachment. L. echigonia is thought to be a suitable host, on which over 10% of attached glochidia metamorphosed to juveniles.