Molluscs from Hydrothermal Vents and Cold Seeps in Japan : A Review of Taxa Recorded in Twenty Recent Years (1984-2004)

Abstract

Molluscs hitherto recorded from deep-sea vent/seep environments in Japan are reviewed and listed based on various literature published up to 2004. Compiled data on holotype depositories and type localities as well as detailed distribution records with geographic and depth ranges, and type of habitat (vents and/or seeps) are given for each of 74 recorded species (2 polyplacophorans, 30 bivalves and 42 gastropods). Comparison of faunas at various localities revealed the following characteristics: 1) The Japanese vent/seep fauna is typified by the highest diversity of Calyptogena in the world. 2) Bathymodiolus is the second most diversified large-sized bivalve in Japanese vents and seeps. 3) Conspecific populations of Calyptogena and Bathymodiolus have been proven to occur both in vents and in seeps, but most other molluscan taxa are obviously either vent-or seep-specific. 4) Two major groups of deep-sea bivalves, protobranchs and anomalodesmatans, are rare or totally absent, in contrast to non-vent/seep environments. 5) Vent/seep-endemic limpets are highly diversified. 6) Neomphalids and peltospirids (so-called 'hot vent taxa') are absent, except for a single species. 7) Among caenogastropods, small-sized provannids (Provanna) are dominant, rather than large-sized ones (Alviniconcha and Ifremeria). 8) Naticid predators have never been found in the Recent fauna, although fossil records suggest their presence in seeps in the geologic past. 9) Some species of neogastropod predators have been reported as temporal invaders from the ambient environment. 10) Two species of chitons from vents in the Okinawa Trough represent the only record of polyplacophorans from chemosynthetic communities in the world. 11) No aplacophorans, monoplacophorans, scaphopods or cephalopods have been collected at Japanese vent/seep sites.