1. The University Museum, The University of Tokyo, Tokyo 113–0033, Japan
2. Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Tokyo 113–0033, Japan
3. Fukui City Museum of Natural History, Fukui 918–8006, Japan
4. Department of Anatomy and Cell Biology, College of Veterinary Medicine, Seoul National University, Seoul 151–742, Korea
5. Korean Otter Research Center, Hwacheon-gun, Gangwon-do 209–821, Korea