Which fact about axolotls is true?
The axolotl (Ambystoma mexicanum) is the best known of the Mexican mole salamanders: it belongs to the Tiger Salamander complex. The Axolotl shows neoteny: the larvae do not undergo metamorphosis, so the adults stay aquatic, with external gills.
A sexually mature adult axolotl, at age 18–24 months, ranges in length from 15 to 45 cm (6 to 18 in).
The axolotl is only native to the freshwater of Lake Xochimilco and Lake Chalco in the Valley of Mexico. Lake Chalco no longer exists, having been drained as a flood control measure, and Lake Xochimilco remains a remnant of its former self, existing mainly as canals.
The feature of the axolotl that attracts most attention is its healing ability: the axolotl does not heal by scarring and is capable of the regeneration of entire lost appendages in a period of months, and, in certain cases, more vital structures, such as tail, limb, central nervous system, and tissues of the eye and heart.
Axolotls exhibit neoteny, meaning that they reach sexual maturity without undergoing metamorphosis. In the axolotl, metamorphic failure is caused by a lack of thyroid stimulating hormone, which is used to induce the thyroid to produce thyroxine in transforming salamanders. Axolotls can be induced to metamorphose by an injection of iodine (used in the production of thyroid hormones) or by shots of thyroxine hormone. The adult form resembles a terrestrial plateau tiger salamander.