STALKED CRINOIDS FROM THE HADAL DEPTHS OF JAPANESE TRENCH AND THEIR IMPLICATIONS FOR SURVIVAL IN "EXTREME ENVIRONMENTS"

Stalked criniods, presumably assigned to Bathycrinus volubilis Mironov, crowdedly live on hard substrates in the hadal depths (8994-9102 m) of northern Izu-Ogasawara Trench, off the eastern coast of Japan. They are regarded as the deepest representative of echinoderms. Living postures of these crinoids were monitored by a remote operated vehicle Kaiko in 1999. Because this species has also been collected in wide areas near the trench axes of northwestern Pacific by the former Soviet Union’s R/V Vityaz, modern crinoids should be regarded as one of the important members in hadal depths of this area. The photos and videos demonstrated that the crinoids have feeding postures comparable to those in shallower depths; making parabolic filtration fans with their mouths oriented down-current. In aquarium experiments using living specimens of an isocrinid Metacrinus rotundus showed that they actively select their food particles over variously sized glass beads, and also control the current flowing through the arms. Therefore, they are not non-selective suspension feeders, but are selective feeders with an efficient food-gathering strategy. In extreme environments such as hadal depths, crinoids presumably use such sophisticated way of feeding to survive in a very nutrient-poor environment. Japanese Miocene bathyal echinoderms from the Morozaki and other groups, and their paleobiogeographic implications are also mentioned in the presentation.