okutani kojima (8 risultati)

The distribution of molluscan species at six cold-seep sites at between 5291 and 6290 m on the landward slope of the Japan Trench was studied using the crewed submersible Shinkai 6500 and the ROV Kaiko. At least four species of bivalve (Acharax johnsoni, Calyptogena phaseoliformis, C. fossajaponica and Parathyasira kaireiae) and three species of gastropod (Retiskenea diploura, Provanna abyssalis, and Provanna shinkaiae) were determined to be endemic to chemosynthesis-based communities. Two gastropod species (Bayerius arnoldi and Admete temuissima) were confirmed to be colonists in chemosynthesis-based communities. The molluscan assemblages were of differing composition at each site. The two dominant bivalves, C. phaseoliformis and C. fossajaponica, showed specific differences in their distributions. C. phaseoliformis was mainly associated with silt sediments, whereas C. fossajaponica dominated the aggregations on pebble substrates. However, in a single case of codominance by both Calyptogena species, almost all individuals were of small size. The small gastropod Retiskenea diploura was found in clusters on the shell surface of C. phaseoliformis and on the silt sediments within the aggregations. This is the first record of a species of the family Neomphalidae from a chemosynthesis-based community in Japanese waters. 12 pp., 9 figs, gr. 8.

Two species of bivalve of the genus Vesicomya were collected by the submersible Shinkai 6500 and the ROV Kaiko from chemosynthetic environments in upper abyssal depths in the western and central sectors of the Nankai Trough, extending from off Shikoku to off western Honshu, Japan. They are Vesicomya crenulomarginata n. sp. and large specimens of V. kaikoae Okutani, Fujikura & Kojima, 2000. Besides five known species of Calyptogena collected, another new species of the same genus Calyptogena (Archivesica) magnocultellus n. sp. was found and is described here. Ontogenic and individual variabilities in C. (Ectenagena) nautilei are discussed. 12 pp., 6 figs, gr. 8.