axolotl

axolotl , a salamander , Siredon mexicanum, found in certain lakes in the region of Mexico City, which reaches reproductive maturity without losing its larval characteristics. This phenomenon is called neoteny; in salamanders it is apparently caused by certain environmental conditions, particularly a low level of iodine in the water, which affect the functioning of the thyroid gland. Axolotls are permanently aquatic, never undergoing the metamorphosis to a terrestrial form characteristic of amphibians. They grow larger than ordinary larval salamanders and develop sexually, but they retain external gills and a well-developed tail. The axolotl was not recognized as a salamander until 1865, when several specimens at the Jardin des Plantes in Paris suddenly underwent metamorphosis. After some experimentation it was discovered that when their pools were dried up most of the animals changed into the adult form. Axolotls will also mature normally if fed thyroid gland extract. The related North American tiger salamander, Abystoma tigrinum, often exhibits neoteny in the Rocky Mts., where the iodine content of the water is low. The axolotl has a broad head and bushy gills; its skin is a black-speckled dark brown. It may grow as long as 13 in. (33 cm). In Mexico City, axolotls are sometimes cooked and eaten as delicacies. They are classified in the phylum Chordata , subphylum Vertebrata, class Amphibia, order Urodela, family Abystomidae.

axolotl Larval form of certain species of salamander native to w USA and Mexico. Axolotls are aquatic amphibians that normally mature and reproduce without developing into adult salamanders. Length: c.25cm (10in). Family Ambystomidae.

Ambystomatidae (mole salamanders, axolotls; class Amphibia, order Urodela) A family of amphibians which have a broad head, the tongue free only at the sides, palatal teeth, costal grooves down the body, short, strong limbs, and a laterally compressed tail. Most burrow in earth for much of the year. Neoteny is common in some species, the best-known example being Ambystoma mexicanum (axolotl), confined to certain lakes around Mexico City, which normally breeds as an aquatic larva, but is capable of metamorphosis into a terrestrial form; it is sexually dimorphic, the female being the larger, attaining up to 29 cm in length, and normally black although albinos are not uncommon. There are more than 30 species, found in N. and Central America.