Axolotl

The Mexican axolotl or salamander, Ambystoma mexicanum, is a salamander with the unusual characteristic of retaining its larval features in its adult life. This condition, known as neoteny, means that it retains its tadpole-like dorsal fin - which runs almost the entire length of its body - and its external gills, which protrude from the back of its broad, feathery head.