The Mexican axolotl (pronounced ACK-suh-LAH-tuhl) salamander has the rare trait of retaining its larval features throughout its adult life. This condition, called neoteny, means it keeps its tadpole-like dorsal fin, which runs almost the length of its body, and its feathery external gills, which protrude from the back of its wide head.
Axolotls are used extensively in scientific research due to their ability to regenerate limbs.
As of 2010, wild axolotls are near extinction due to urbanization in Mexico City and polluted waters. Non-native fish, such as African tilapia and Asian carp, have also recently been introduced to the waters. These new fish have been eating the axolotls' young, as well as its primary source of food. The axolotl is currently on the International Union for Conservation of Nature's annual Red List of threatened species.