Introductionsalamander, an amphibian of the order Urodela, or Caudata. Salamanders have tails and small, weak limbs; superficially they resemble the unrelated lizards (which are reptiles), but they are easily distinguished by their lack of scales and claws, and by their moist, usually smooth skins. Salamanders are found in damp regions of the northern temperate zone and are most abundant in North America. Most are under 6 in. (15 cm) long, but the giant salamander of Japan ( Megalobatrachus japonicus ) may reach a length of over 5 ft (1.5 m). Most salamanders are terrestrial as adults, living near water or in wet vegetation, but some are aquatic and a few are arboreal, burrowing, or cave-dwelling. Most are nocturnal, and all avoid direct light. Salamanders are able to regenerate a lost limb or tail. They feed on small animals, such as insects, worms, and snails.
Most salamanders breed in water and are gregarious at breeding time, when there is usually a courtship display. In most species fertilization is internal. The male deposits sperm packets, which the female picks up with the cloaca; the sperm is then stored until fertilization takes place. The eggs, surrounded by gelatinous material, are usually laid in ponds or brooks, where they develop into aquatic larvae that can breathe by means of gills. A few salamanders breed on land, laying their eggs under rotting vegetation; the young pass through the gilled stage in the egg, emerging as miniature adults. Such strictly terrestrial forms are the red-backed salamander ( Plethodon cinereus ) and slimy salamander ( P. glutinosus ) of E United States and the slender salamander ( Batrachoseps attenuatus ) of the Pacific coast.
Most salamanders, including most that remain in an aquatic environment, go through a typical amphibian metamorphosis into air-breathing adults. Generally the adults have lungs, but in the large family of lungless salamanders (Plethodontidae) breathing occurs entirely through the skin and the lining of the throat. In a few salamanders growth occurs without metamorphosis, and the gilled, juvenile form is able to reproduce. This phenomenon (called neoteny) is found in the sirens (family Sirenidae) of S United States and N Mexico, in the mud puppies (family Protidae), and in the Mexican axolotl. It may also occur in the Western varieties of the North American tiger salamander ( Ambystoma tigrinum ) under certain environmental conditions. The newts are a large, widely distributed family of salamanders; North American species include the red-spotted newt, which goes through a terrestrial stage known as the red eft.
The North American blind salamanders (several genera in the family Plethodontidae) live in underground streams, caves, and wells in S United States. As adults they have whitish, translucent skin, which covers their eyes. The olm is a European blind salamander related to the mud puppy. The giant salamander ( Dicamptodon ensatus ) of the NW United States grows to 12 in. (30 cm) in length. The hellbender ( Cryptobranchus alleganiensis ) of E United States and the so-called Congo eel ( Amphiuma means ) are large aquatic species. The former, of the same family as the Japanese giant salamander, grows to 20 in. (50 cm); the latter, slender and eellike in appearance, with tiny legs, may reach 30 in. (75 cm).
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