Large populations of two new species of Ophiambix (Echinodermata, Ophiuroidea) discovered on Japanese hot vents and cold seeps.

Two new species and two new occurrence records of the genus Ophiambix Lyman, 1880 (Echinodermata: Ophiuroidea), were found on hydrothermal vents at the Pacific coast of Japan. Ophiambix kagutsuchi, new species, is distinguished from other congeners in having small granules separated from each other on aboral surface of disc, flat teeth, second from oral-most arm spines being cylindrical and spiniform in shape, and one small and spiniform tentacle scale on each tentacle pore. Ophiambix macrodonta, new species, is distinguished from the other congeners in having small granules circularly arranged surrounding the periphery of disc scales on aboral surface of disc, flat teeth, second from oral-most arm spines being flat and leaf-like in shape, and one small and spiniform tentacle scale on each tentacle pore. Furthermore, Ophiambix epicopus Paterson & Baker, 1988, was recorded from Japan for the first time and another congener, Ophiambix aculeatus Lyman, 1880, was also collected. Ophiambix kagutsuchi, new species, and Ophiambix macrodonta, new species, were collected from deep-sea chemosynthetic environments. A tabular key to all six species of the genus Ophiambix is provided. [ABSTRACT FROM AUTHOR]