New additions to the Japanese marine molluscan fauna are here recorded : Neocancilla kayae Cernohorsky, 1978, hitherto known only from the Hawaiian Islands, Vexillum (Costellaria) delicatum (A. Adams, 1853) known from the tropical Indo-West Pacific, and V. (Nodicostellaria) sauternesense Suduiraut, 1997 known from the Philippines. V. (Pusia) charlesi n. sp. was previously known only as an undescribed species from the Philippines, but has recently also been found in Japan and is here described. Thala maxmarrowi Cernohorsky, 1980, originally described from Okinawa, is recorded from the Kii Peninsula, central Honshu.
Assiminea japonica Martens, 1877 is commonly distributed in brackish waters in the Japanese main islands. Some local populations of the snail, however, have been reduced due to recent coastal developments. Distribution of the snail was surveyed along the Hinuma brackish water system and the size distributions of two local populations were monitored between May 1995 and January 1996. The snail was mainly distributed in reedy marshes and gravelly shores, but not on sandy shores or concrete banks. The snails inhabited brackish water where salinity was less than 8‰ and did not inhabit seawater or fresh water. Four shell color patterns were recognized. The ratio of the four shell color patterns within the population was different at every observation site. The snail widely occurred from intertidal to very shallow subtidal bottoms, but most snails did not migrate between these two bottoms during the tidal cycle. Seasonal changes in size composition in two snail populations were very different. A population in a reedy marsh was composed of adult snails throughout the year without recruitment, but a population on a gravelly shore was mainly composed of small juveniles.
Growth of hatchery-produced Iwagaki-oyster Crassostrea nippona suspended at a mean depth of 7 m at Dozen Bay, the Oki Islands, Shimane Prefecture, Japan was examined over 23 months. Means of shell height, weight of whole body, and volume of whole body after hatching, respectively attained 52.2 mm, 25.6 g and 19 cm^3 after 12 months and 106.2 mm, 183.9 g, and 126.9 cm^3 after 23 months. The growth of Iwagaki oysters was affected by spawning, gonad development, low water temperature and possibly food availability inferred from the abundance of phytoplankton. Eleven shell characters : Total shell height, shell height, shell length, shell width, weight of whole body, soft tissue weight, weight of right valve, weight of left valve, volume of valves, volume of whole body, and volume of inner space were measured, and analysis was carried out to determine which characters best represent growth in whole body volume. The results showed that weight of the whole body and weight of the left valve were the most representative, but suggested that shell height was the most convenient for practical use.