The pyramidellid gastropod Odostomia oyasiwo Nomura, 1939 was originally described using specimens collected in northeastern and central Japan. In 1997, more specimens were obtained from off the Kii Peninsula, and we herein re-describe O. oyasiwo on the basis of both sets of material. Shell morphology is compared in detail with a confusingly similar species, Odostomia desimana Dall & Bartsch, 1906. All the live-collected specimens examined in the present study were found on the shell of Fusinus perplexus (A. Adams, 1864), although it is not possible to determine whether this pyramidellid actually parasitizes F. perplexus without further observing the behavior of living O. oyasiwo.
Two closely related batillariid snails, Batillaria multiformis and B. cumingi, commonly occur together on tidal flats around Tokyo Bay. During the last decade, however, local populations of B. multiformis have declined precipitously or become extinct, while those of B. cumingi have remained stable or even increased. The results of this research, which consisted of population status surveys of the batillariid snails in an enclosed tidal flat in Tokyo Bay and a rearing experiment of B. multiformis, suggest that the differences in status between these two species could be explained in terms of their respective life cycles ; while B. multiformis produces egg capsules that hatch into planktonic larvae, B. cumingi spawns isolated eggs that hatch out as benthic juveniles. Since the late 1960s, extensive coastal landfill has eliminated most of the tidal flats and salt marshes that originally formed a continuous ring around the Tokyo Bay shoreline. Only a few suitable tidal habitats remain, and these are isolated from one another. The planktonic larvae of B. multiformis may thus be unable to drift to a suitable habitat for settling out. In addition, severe bottom hypoxia occurs in the bay during the summer months, when the larvae are released, and this may adversely effect their survival rate. In contrast, the benthic juveniles of B. cumingi are able to recruit directly on their parent tidal flats, which are not impacted by the coastal landfill or hypoxia, making it easier for them to maintain or expand their local populations.
In order to aid specific identification of the larvae (D-shaped and umbo larvae) and post-larvae of the two tropical Modiolus species M. auriculatus and M. philippinarum common in shallow waters around Okinawa, southern Japan, we describe and compare the morphological features of their shells based on larvae and post-larvae reared in the laboratory observed with optical microscope and SEM. The umbo larvae of M. philippinarum are distinguishable from those of M. auriculatus by differences in hinge morphology, shell color, and the size of the shell at the time when eyespots appear. The post-larvae of M. philippinarum are also distinguishable from those of M. auriculatus by differences in hinge morphology, shell color and the size of shell at the time when primary lateral teeth and periostracal hairs appear. The umbo larvae of Modiolus species (M. auriculatus, M. philippinarum and M. modiolus) are not distinguishable from those of other genera in the Mytilidae described in past studies, except that the umbo larvae of Perna possess primary lateral teeth. The post-larvae of the above Modiolus species are distinguishable from those of other genera in the Mytilidae described to date by a combination of the three types of lateral teeth, bearing only primary lateral teeth.
We surveyed distributions of Bradybaena pellucida and B. similaris in the Boso Peninsula. B. pellucida is known to occur discontinuously in western Japan and in a limited area around Tateyama, at the southern end of the Boso Peninsula. B. similaris is cosmopolitan, distributed on most islands of Japan. The two species are closely similar to each other in shell and genital morphology, except for the color of the mantle surface, which is visible through the shell. We have found that B. pellucida predominantly occurs across the southern Boso Peninsula and is sympatric with B. similaris at several localities. B. similaris is dominant north of the range of B. pellucida.
Activity rhythms, homing and reproductive behaviors of the hermaphroditic pulmonate mollusc Peronia verruculata (Cuvier, 1830) were investigated on a rocky intertidal zone on Sesoko Island (26°38′N, 127°54′E), Okinawa. The molluscs stayed in holes in the rock while the habitat was submerged or washed with seawater. Animals emerged and were active only when their habitats were completely exposed. All individuals showed homing behavior. The number of emerged individuals, the distance moved and the duration of excursions were inversely related to the lowest tidal level at ebb tide. Animals that emerged were fewer and less active at night than during daytime. Initial courtship of individuals as males was seen 21 times, and in 5 cases copulation occurred. Peronia verruculata (Cuvier, 1830) played a positive role as males but a passive role as females in courtship behavior and copulation.
The oviparous snail Cerithideopsilla djadjariensis (K. Martin, 1889) is distributed on tidal flats in south-west Japan. Seasonal changes in the distribution of C. djadjariensis were studied in the world's northernmost mangrove forest at the mouth of the Atago River in southern Kyushu Island. Four gastropod species : Batillaria multiformis (Lischke, 1869), Cerithideopsilla djadjariensis (K. Martin, 1899), Cerithideopsilla cingulata (Gmelin, 1791) and Cerithidea rhizophorarum A. Adams, 1855, show sympatric distribution in this area. Newly recruited juveniles (3-6 mm shell length) of C. djadjariensis appeared from August to November. To established the main habitat of the four species, the substrate on the tidal flats was classified into six types ; gravel, sandy gravel, sand, muddy sand, sandy mud and mud. From the patterns of distribution of the four species on the tidal flat, C. djadjariensis prefers sandy mud and muddy sand ; B. multiformis prefers sandy gravel and sand, and C. cingulata prefers the muddy sand and mud. Stomach contents were observed under a fluorescent microscope with a rhodamine filter in order to determine the food preference among the four species. It is suggested that Cerithidea rhizophorarum has a stronger preference for algae than the other three species.
Seasonal changes in size and density of the three bivalve species, Acropsis (Galactella) symmetrica (Reeve, 1844), Barbatina (Abarbatia) lima (Reeve, 1844) and Cardita leana Dunker, 1860 were studied in the intertidal area on a lava seashore in southwestern Japan. These three species are distributed sympatrically on a boulder shore on Sakurajima Island (31°35′N, 130°36′E) in Kagoshima Prefecture, Kyushu, Japan. Juveniles (<3 mm shell length) of A. symmetrica were frequently observed from September to December. A. symmetrica seems to be an annually-reproducing species. In B. lima, juveniles were observed from August to March. Juveniles of C. leana were observed in April and from October to December. Frequency distributions of shell size suggest lifespans for B. lima and C. leana to be more than one year. B. lima was found distributed widely from the lower to the middle zones, while the other two species were limited to the lower zone. It was estimated that most of the newly settled juveniles of B. lima died in the middle zone. The density of B. lima was greatest in the middle zone in June, and in the lower zone in November.
Preservation of molluscan specimens for DNA analysis is one of the most important collection management issue in modern malacology. The merits and demerits of two simple methods of DNA preservation, storage in ultracold freezer and alcohol preservation, are compared. Preferred protocols for alcohol preservation are described.