The paleontological study on the origin and evolutin of submarine cave ostracodes from coral reefs.

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The puropose of this study is to reveal the faunal characteristics of the submarine cave ostracodes from the Ryukyu Islands, and the evolutionary process of the new troglobitic saipanettid genus.The characteristics of the cave assemblages from "Daidokutsu" of Ie Island are enumerated as follows. (1) Living individuals are very rare. The rare occurrence of living ostracodes probably reflects the oligotrophic conditions of submarine caves. (2) The ostracode assemblages from "Daidokutsu" consist mostly of shallow water elements from outside the cave. Exceptionally, three saipanettid species, including 'new genus' (1sp.), are all thought to have derived from deep-sea ancestors. (3) Cytheraceans from the "Daidokutsu" samples are relatively low in species diversity and individual abundance compared to other ostracode taxa. The ostracode assemblages from various habitats of open sea floor environments have been dominated by cytheraceans since the middle Jurassic.A new troglobitic saipanettid genus, only found from submarine caves of the Ryukyu Islands, possibly derived from the saipanettid Cardobairdia, a deep-sea muddy bottom inhabitant, or its relatives. It is likely that the new genus has successfully colonized hard substrata in caves, particularly exploiting the crevices on cave walls and ceilings as its microhabitat. The new genus may have adapted to this cryptic habitat in response to strong cytheracean competetors, and to predators such as gastropods that do not survice well in dark and oligotrophic submarine caves. Insofar as well preserved appendages have been investigated, the new genus differs from the closely related genera Saipanetta and Cardobairdia in having fewer setae without any fine structure. While crawling, the new genus keeps its carapace widely gaped. The ability to open the carapace widely is one of the primitive behavioral features of podocopids.