The axolotl is famous for regenerating lost limbs and several other body parts.
Unlike most amphibians, axolotls usually remain in their larval, aquatic form throughout life, retaining external gills and a finned tail. This condition is called neoteny. Their regenerative ability allows them to regrow limbs, parts of the spinal cord, heart tissue, and sections of the brain without the heavy scarring typical of adult mammals.
Axolotls are native to the lake and canal system around Mexico City, especially the remaining habitat at Xochimilco. Wild axolotls are critically endangered because of habitat loss, pollution, invasive fish, and urban pressure, although captive populations are common in laboratories and aquariums.
The species is Ambystoma mexicanum. It is often mistaken for a fish because of its aquatic appearance, but it is an amphibian. Regeneration is not unlimited: the replacement structure must still form under suitable biological conditions.