Four protobranchiate bivalves were collected by the ROV Kaiko from hadal depths in the Japan Trench in July 2002. They are Katadesmia vincula, Neilonella profunda n. sp., Ledellina convexirostra and Yoldiella kaikonis n. sp.
Pseudotalopia fernandrikae n. sp. is described from the Philippines and compared with similar trochid species from the Indo-Pacific. The new species is mainly diagnosed by tumid whorls, a rounded periphery, a deep umbilicus, about 10 main spiral cords and only a few weaker additional cords, of which only the most adapical are granulate.
A new ovulid species, Primovula oryza, is described from off the Kii Peninsula, the Kurose bank near Hachijo-jima Island in the Izu-shichito Islands, and Tatsumi-dashi in the Ogasawara Islands, all in Japan. It is most similar to Primovula dorsuosa (Hinds, 1844) in morphology, but it can be distinguished by non-crenulate anterior extremity, beaked posterior extremity, and different line marking on the dorsum. In addition to this description, Dentiovula colobica Azuma & Gate, 1971 is designated as the type species of the genus Dentiovula.
Two species in the fasciolariid genus Fusolatirus Kuroda & Habe, 1971 from Japan are examined. F. coreanicus (E. A. Smith, 1879) is redescribed from the type material. The species misidentified by Habe (1961) as F. pilsbryi (Kuroda & Habe, 1952; = F. coreanicus) is recognized as distinct and described as F. higoi n. sp. It is further compared with F. rikae (Fraussen, 2003), a Philippine species described in the buccinid genus Euthria that is here reassigned to Fusolatirus. Two specimens from the same lot as the holotype of F. higoi are provisionally described as Fusolatirus sp.
A new species of the genus Lurifax is described from Sumisu Caldera, southern Japan. It is the second Recent species of the genus and the first record from the Northwest Pacific, following L. vitreus Waren & Bouchet, 2001 from the Mid-Atlantic Ridge and the Mediterranean. The two species are distinguished from each other by the form and sculpture of the teleoconch whorls.
A small school of the bobtail squid Heteroteuthis hawaiiensis was observed on the ocean floor at a depth of 912m near the Ogasawara Islands. This is the first report of an observation on the living deep-sea bobtail squid.
The embryonic and larval development of the trochid gastropod Umbonium moniliferum (Lamarck, 1822) is described, based on material reared in filtered seawater at 22.6-25.1℃ in the laboratory. Fertilized eggs were obtained via artificially induced spawning of adults collected from an intertidal sand flat in southern Japan in October 2002. Each egg was 170μm in diameter, surrounded by a vitelline membrane and a gelatinous coating. The trochophore larvae hatched at 6h after fertilization, and became veliger larvae at 8h, with the completion of the velum. At 48h, the larvae began to crawl on the substratum and swim in the water column alternately. Metamorphosed larvae (= juveniles) of 200-μm shell width appeared at 200h, with the velum lost. This was induced by the provision of sediment inhabited by adults and seawater agitation. The reported time for larvae of the other two congeneric species to reach the metamorphosis is shorter [48h in U. vestiarium (Linnaeus, 1758) at 28-30℃; 3d in U. giganteum (Lesson, 1833) at 20℃]. The longer time required in the present case could reflect delayed metamorphosis due to lack of more appropriate stimuli.
Seasonal changes in size and density of a potamidid snail, Cerithidea cingulata (Gmelin, 1790), were studied on a tidal flat neighboring the mangrove forest at the mouth of the Atago River, southern Kyushu, Japan. Juvenile snails smaller than 2mm in shell width occurred from October through May, suggesting recruitment during this period. The proportion of snails with lips retroflexed was higher at the upper site than at the lower site. The seasonal change in size structures suggests that it takes two years for juveniles to become large-sized snails with retroflexed lips.
Seasonal changes in growth and abundance of the trochid snail Cantharidus japonicus on thalli of the brown alga Sargassum ringgoldianum were studied from June 2001 to May 2002 in Odawa Bay, eastern coast of Sagami Bay, central Honshu, Japan. The density of individuals reached its maximum in June, when the plant length of S. ringgoldianum was decreasing, and fell to a minimum in February when the plant length was increasing. The seasonal changes in abundance of C. japonicus followed the changes in S. ringgoldianum with a lag of two months. Newly settled juveniles of C. japonicus appeared in May and November, and grew rapidly thereafter. The longevity of the snails was estimated to be 18-20 months.