Taxonomical and Paleoenvironmental Study of Genus MELONIS (Benthec Foraminifera)

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The genus Melonis, which is a calcareous benthic foraminiferal genus and regarded as an indication of deep-sea bottom water in the Quaternary to Recent, is exmained taxonomically and paleoecologically.The taxonomy and intraspecific variations of the genus in the Northwest Pacifec are biometrically examined based on the specimens from four piston-cores collected from off Shikoku, near the Daito Ridge, east of Ogasawara Islands and near the Shatsky Rise. Several reference materials are used for the taxonomic comparison. They are a few rescent sediments from the equatorial Pacific Ocean and Okhotsk Sea and some reference areas including the Mediterranean region.As a result, Melonis sphaeroides, M. affinis, M. SP. A and M. barleeanus are identified in the late Pleistocene to Holocene sequences of the Piston-cores. The inflated form of the genus is distinguished from the typical M. pompilioides in the Mediterranean region. Melonissphaeroides contains a cold -water variety, which is found in the two shallower sites. This variety is living in the Okhotsk Sea.Melonis affinis, characterized by very finely perforated wall, is found only in the two deeper sites Melonis barleeannus has wider variation on the degree of limbate wall, form (typical M. barleeanus to much limbate one M. nicobarensis-form). The latter form has been identified as M. parkerae by some authors.A lot of samples have been collected to recognize distribution of fossil species. In this moment, specimens of Melonis have been found in the upper Eocene to lower Pleistocene from Hokkaido to Okinawa. Those taxonomic study is performed continuously.