| Research Abstract |
The systematic study of the Class Hydrozoa (PhylumCnidaria) in the Nansei Islands has been conducted during 1992-1994. The collection of materials and field work was done at 36 stations on seven islands (Amami-oshima, Okinawa Island, Aka Island, Miyako Island, Ishigaki Island, Kuroshima Island, Iriomote Island) and through laboratory-rearing hydromedusae of 47 species of 39 genera (7 orders) and hydropolyps of 27 species of 21 genera (2 orders) were recognized. Together with hydropolyps of 30 species of 25 genera (2 orders) which were already reported from mainly shores of Okinawa Island, a total of 82 species of 67 genera (seven orders) are distributed in Nansei Islands, showing a rich hydrozoan fauna in this study area. All hydromedusae collected in the present study are the first record in this area. Among them, 13 species are new to Japan or unidentified, and the growth, cnidome, gametes, and larva of most of these medusan species were clarified. Further, range of individual variation and biogeographical data were compiled together with former records. Most of the hydrozoans collected in the Nansei Islands are also distributed in any given area from kyushu to Hokkaido, and at present hydromedusae of 11 species and hydropolyps of 4 species are exclusively distributed in the Nansei Islands. It is known that hydromedusa fauna in the Nansei Islands are similar to that of Taiwan Strait and around Amoy, China where the taxonomic study of hydromedusae were well studied.
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