| Research Abstract |
1. Submarine cave organisms from Naisei and Daito Islands were investigated with the help of some SCUBA diviers. Base on the samples from the submarine caves of these islands as well as those collected from the Oagasasawa, Palau and Philippines Islands, I discussed the primitiveness and origin of the submarine cave organismas with special reference to the molluscs.
2. In addition to the unique specific composition, common significant characteristics of the submarine cave bivalves in northwest Pacific are (i) reduced adult shell size (less than 5 mm), (ii) transparent or semi-transparent coloreless shells、(iii) many epifaunal and semi-infaunal species, (iv) many deepwater genera, (v) frequent paedomorphosis by progenetis, and (vi) low fecundity and dominance of brooding.
3. Submarine cave gastropods also includes many genera most known from deepwaters. In view of early developnent, submarine cave archaeogastropods shows direct development or short-term swimming larvae, but the meso-and neogastropods are planktotrophic and pelagic larvae, the situation different from the bivalves.
4. While the submarine-cave bivalve species seem to be limited mostly to shallow-water, cryptic environments, the submarine-cave gastropods are commonly known from the neighboring deepwater bottoms, suggesting different origins between the two groups.
5. The bivalves and gastropods in the submarine caves show shell architectures and life styles that were dominated in Paleozoic and Mesozoic shallow-water bottoms, indicating primitivenes ecologically rather than taxonomically. Infrequent predation in the submarine caves seems to be one of the factors for estaglishing this unique biota, the condition similar to shallow-water marine bottoms before 'Mesozoic Marine Revolution'.
|
