Examination of the type specimens of Teinostoma (Calceolata) pusillum (C. B. Adams, 1850) from Jamaica revealed that the species should be reallocated to Neritilia Martens, 1879 (Neritopsina : Neritiliidae). The species is characterized by an inclined protoconch and a minute, neritiform teleoconch with a straight, edentulous inner lip, both features typical of Neritilia. Calceolata Iredale, 1918, the genus established for the present species, is therefore regarded as a junior synonym of Neritilia. The lectotype of Neritilia pusilla is herewith designated.
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.
Activity patterns of the herbivorous gastropod, Monodonta labio, were observed in a single population on a gently sloping boulder shore at Amakusa, west Kyushu, Japan, in summer. Intraspecific variations of the activity patterns related to the level on the shore and the size of the snails were recognized. Snails were divided into three size classes : large (shell width>13 mm), intermediate (9-13 mm) and small (≦9 mm). Snails moving on the upper surface of the boulders were considered as 'active', while those not moving but staying on the surface as 'stationary'. The other snails, which were resting on the underside of the boulders, were not counted. In all the intertidal zones, many snails of all the three size classes were active during awash (affected by wave action) conditions both in the daytime and the nighttime and during the nighttime emerged (exposed to air) condition. In addition, the large snails were active when submerged in the nighttime in the mid and low intertidal zones. In the mid zone, the activity of the intermediate and small snails during the daytime awash condition tended to be lower than during the nighttime awash and emerged conditions. Some of the snails were stationary on the surface of the boulders while emerged during the nighttime. When emerged during the daytime, however, almost all the snails were inactive.
We studied population dynamics and life history traits of Siphonacmea oblongata living on seagrasses in Otsuchi Bay, the first record of this species from Honshu. Field census was conducted from October 1995 to November 1996 at intervals of 1-1.5 months. The limpet was collected quantitatively from both Zostera marina and Zostera caulescens patches in a single seagrass bed. S. oblongata undergoes benthic development, settling on seagrass leaves directly after developing in an egg-mass. The recruitment occurred from spring to early summer, while the previous-year class decreased during this period and totally disappeared in summer, indicating an annual lifespan for Siphonacmea. The density increased rapidly from May to June due to recruitment, remained high during summer, and drastically decreased from August to October. The increase in abundance occurred in accordance with the increase in seagrass biomass and high biomass of epiphytic microalgae in Z. marina patches. The dramatic decline of abundance from August to October may be caused primarily by food shortage because limpet growth became slow during this period as biomass of epiphytic microalgae decreased. The abundance of S. oblongata was significantly lower on Z. caulescens than Z. marina throughout the year. Recruitment rate was very low on Z. caulescens. The results indicate that S. oblongata prefers Z. marina as a habitat to Z. caulescens. The habitat preference may be related to the morphological characters of Z. marina, such as non-branching vegetative shoots dominating throughout the year, and its continuous vegetation pattern with high shoot densities. Seasonal variation in life history traits of S. oblongata also corresponds better to the phenology of Z. marina than Z. caulescens.
We studied the larval recruitment processes of the mytilid Musculista senhousia, by which benthic populations form and are maintained. We analyzed the processes based on the data for densities of different life stages (planktonic larvae, new settlers, and small to large bivalves) collected on the two tidal flats Kawaguchi and Nameishi (20 km apart) in the Ariake Sound for 2 years. Throughout 2 years observation, density of all stages was higher at Kawaguchi than at Nameishi except for large bivalves in 1998. We suggest that the higher density of large bivalves at Kawaguchi may be driven by a higher density of larvae.
Donacidae and Mesodesmatidae are bivalve families that characterize the intertidal zone of beaches in the Japanese Islands. Substrate preferences and burrowing ability were analyzed for all four species of Donacidae and five selected species of Mesodesmatidae that occur on the beaches of Southwest Japan from the Ryukyu Islands to Kyushu, Shikoku and western Honshu. Both families are generally similar in habitat and other ecological characteristics, but the Donacidae is adapted to relatively well-sorted substrate that can be easily fluidized and is favorable for quick burrowing mainly on dissipative beaches exposed to the open sea. On the other hand, members of the Mesodesmatidae inhabit generally more poorly-sorted, coarsergrained substrates of reflective beaches in bays or those sheltered by coral reef, which is unfavorable for quick burrowing. This relationship exists in both temperature or subtropical (Kyushu, Shikoku and Honshu) and tropical (Ryukyu Islands) regions. In temperate or subtropical regions, the donacids Chion semigranosus, Latona cuneata and Tentidonax kiusiuensis are common on very well to moderately well-sorted, medium sand of highly exposed to moderately exposed beaches, while Coecella chinensis and other mesodesmatids are abundant on moderately to poorly sorted, coarser-grained substrates of moderately sheltered to highly sheltered intertidal zones. In the tropical Ryukyu Islands, most of the beaches are sheltered by coral reefs, and the poorly-sorted coarse-grained substrates of such beaches are inhabited mainly by mesodesmatids such as Atactodea striata. Better-sorted sediments are inhabited by the donacids Latona faba and L. cuneata. Burrowing abilities measured by a Burrowing Rate Index, which normalizes burrowing time for a specimen mass, are consistent with these substrate and environmental preferences ; members of Donacidae burrow much faster than Mesodesmatidae in both temperate or subtropical and tropical regions.
Sulfur nutrition of gastropods and bivalves relevant to the mangrove ecosystem from central Sumatra, Indonesia was studied using stable isotopic signature (^<34>S/^<32>S ratios as commonly designated by δ^<34>S notation, per mil deviation relative to Canyon Diablo troilite, CDT). The mangroves (Rhizophora mucronata, R. apiculata and Bruguiera gymnorrhiza) assimilate light sulfur (^<32>S) (δ^<34>S=-14.4 to -6.2‰) from among sulfides in the substrate sediments (^<34>S=-20.3 to -11.9‰). The sulfides derive from the reduction of seawater sulfate by activity of sulfate-reducing bacteria under an ample supply of organic matter from mangrove trees. The gastropods (Terebralia palustris, T. sulcata and Telescopium sp.), which feed on the litter of the associated mangroves at low tide, have low δ^<34>S values ranging from -2.5 to +9.5‰ in their soft tissues. The present data indicates that of the sulfur assimilated by these species, 40-70‰ is derived from mangroves, with the remainder coming from sulfates in ambient seawater (δ^<34>S=+21‰), the absolute end-member of sulfur reservoir for marine organisms. The isotopic data provide an overall figure for sulfur nutrition that is difficult to estimate by conventional observation. The common bivalve (Anadara sp., δ^<34>S=+10.3‰) and a gastropod (Strombus (Euprotomus) aurisdianae, δ^<34>S=+14.4‰) obtained from areas of no vegetation in the peripheral regions of the mangrove forests also indicate assimilation of isotopically light sulfur. The isotopically light sulfur would be derived from mangrove leave litter as suspended detritus.
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.