1. Department of Natural History Sciences Graduate School of Science Hokkaido University Sapporo 060‐0810 Japan
2. Department of Chemistry, Biology and Marine Science Faculty of Science University of the Ryukyus Nishihara 903‐0213 Japan
3. Department of Ocean Sciences Tokyo University of Marine Science and Technology 4‐5‐7 Konan, Minato‐ku Tokyo 108‐8477 Japan
4. Research Center for Inland Seas Kobe University 1‐1 Rokkodai, Nada‐ku Kobe 657‐8501 Japan
5. Usa Marine Biological Institute Kochi University 194 Inoshiri Usa, Tosa, Kochi 781‐1164 Japan
6. Department of Biological Sciences Faculty of Science Hokkaido University Sapporo 060‐0810 Japan