As paleontological investigations place increasing emphasis on lateral and vertical biofacies variation of ancient sediments, a need for more critical examination of Recent sedimentary processes and faunal distribution of ostracods is becoming apparent. In order to clarify paleontology and sedimentary environments of Pleistocene marine,brackish, and fresh water sediments distributed along the Pacific Coast of central Japan, a basic examination of Recent sediments from similar environments has been undertaken. Recent sediments suitable for such examination are found in the Hamana-ko Bay which occupies the central area of distribution of these Pleistocene sediments and contains a wide variety of sediments, some of them directly comparable to those of the Pleistocene. The Hamana-ko Bay, situated in the western part of Shizuoka Prefecture, is the largest brackish water embayment (polyhaline) on the Pacific Coast of Japan. The bay covers an area of about 79 km² and connects with the Pacific Ocean (Enshu-nada Sea) through a narrow entrance approximately 200 m wide. The relationship between the various sediments and the corresponding sedimentary environments of the Hamana-ko Bay was analyzed by Ikeya and Handa (1972); the faunal analysis of foraminifers was given in Ikeya (1977).

This paper is a part of a reconnaissance study intended to examine the relationship between the environment and ecology of benthic organisms. Although the standing crop size of ostracods is very small in comparison with that of foraminifers, ostracods occur in a wide range of marine, brackish, and fresh-water environments; thus, ostracods have already been shown to be very useful as indicators for analysis of the sedimentary environments of ancient sediments. The object of the present study is to determine the factors that influence the distribution of Recent ostracod species and to evaluate the value of ostracods as indicators for the interpretation of ancient environments.