The axolotl is a paedomorphic salamander, one that matures without undergoing metamorphosis into the terrestrial adult form; adults remain fully aquatic with obvious external gills. This trait is somewhat unusual among amphibians, though this trait is not unique to axolotls, and this is apparent as they may be confused with the larval stage or other neotenic adult mole salamanders, such as the occasionally paedomorphic tiger salamander widespread in North America; or with mudpuppies, which bear a superficial resemblance but are from a different family of salamanders.