| Definition: | | Ambystoma mexicanum, a type of salamander native to Mexico and the Western United States which spends all of its life underwater. Even as an adult animal, the axolotl retains many larval features, most notably its external gills: as a result the axolotl is an excellent example of the phenomenon of neoteny. The axolotl also has four legs and a tadpole-like tail and is an endangered species. |