TIL that axolotl are neotenic.[0] There are rare instancea of axolotl going through metamorphosis to become terrestrial. However, if this occurs after sexual maturity the axolotl will not survive more than one or two years.[1]
[0] "axolotl ... is a neotenic salamander related to the tiger salamander." Wikipedia
[1] http://www.axolotl.org/tiger_salamander.htm
Another neotenic salamander species is the Olm[0], which is an old world species that is blind and lives in caves.
