the aquatic larvae of the species. Measurements of head size and tail shape for the paedomorph-like males produced results intermediate between adult males and larvae. Two of the three males also exhibited three small external gill ramus pairs and vomerine teeth arranged in an inverted “V” as seen on H. retardatus larvae. The same two males also had mobile spermatozoa, confirming that they had already reached sexual maturity and were, thus, paedomorphic. Physiology H. retardatus possess a rare trait among amphibians where the transition from larval hemoglobin to the adult type occurs independently of thyroid activity and can occur for up to two years, well past the actual metamorphosis period. During early stages of development, the liver of H. retardatus is the main erythropoietic organ. The spleen then takes over further into development but before the hemoglobin transition. After the transition the spleen resumes its function as the main source of erythropoiesis, and it continues to do so throughout the life of an H. retardatus individual. The transition from juvenile to adult hemoglobin also occurs entirely within a single population of red blood cells, in contrast to the complete replacement of red blood cells from larval to adult type found in many other amphibian species. A similar method of hemoglobin switching has been seen in mice. Conservation Ezo salamanders are commonly sold through the internet as part of the pet trade. They are also endangered by the introduction of invasive species, as seen in the extinction of the Lake Kuttara population likely due to the introduction of salmon into the lake. Raccoons, a non-native species introduced to Japan by humans, are known to prey upon H. retardatus. Urbanization and modification of wetlands and similar habitats have caused population decline for Ezo salamanders living in habitats in close proximity to humans. References Hynobius Amphibians described in 1923 Endemic amphibians of Japan Taxonomy articles created by Polbot Taxa named by Emmett Reid Dunn