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.