Paleobiological research on the history of earth organisms modeled by the submarine cave ecosystem

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1. We systematically described two new species of mysid crustaceans and one new genus and three new species of neritilid gastropods.2. A unique ecological feature in submarine caves is the infrequency of predator animals, reminiscent of the mid-Mesozoic shallow marine ecosystem. To compare the ecological features between the modern submarine caves and mid-Mesozoic shallow marine ecosystem, we studied the history of shell-drilling, predatory naticid gastropods as they represent the best fossil records of predator-prey relationship. We showed that naticids first appeared in the end of Cretaceous and started drilling predation since that time. On the other hand, we examined drilling and crushing predation in shells of two submarine caves of Okinawa, southern Japan as low as 5%, the frequency is equivalent to those for the late Cretaceous shallow marine assemblages. This is the first documentation of predatory activity in submarine caves.3. Neritilia cavernicala n. sp. was described from anchialine caves of two islands separated more than 200km apart in the Philippines. We presented the first genetic structure for anchailine cave organisms (mitochondrial cytochrome oxidase I), which shows no evidence of genetic isolation between the islands. All individuals are part of a panmictic population and their seemingly isolated cave habitats do not limit gene flow in this species. Larval dispersal may be widely applicable to anchialine stygobites with insular distributions.4. A taxonomic study of Nerilitidae shows the species diversity is the highest in SE Asian islands and becomes smaller in accordance with the distance from the diversity center. Contrast to the previous, widely accepted view that cavericolous animals dispersed primarily by plate tectonics and vicariance, transoceanic dispersal should have played an important role, like most modern invertebrates in tropical coral-reef seas, in forming the present distribution of the cavericolous neritilids.