1. Norwegian Polar Institute, c/o Zoological Museum, P.O. Box 1172 Blindern, N‐0318 Oslo, Norway
2. Department of Ecology and Systematics, Graduate School of Agriculture, Hokkaido University, Sapporo 060‐8589, Japan
3. Department of Polar Science, The Graduate University for Advanced Studies, National Institute of Polar Research, Itabashi‐ku, Tokyo 173‐8515, Japan