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amphibian, in zoology
amphibian, in zoology, cold-blooded vertebrate animal of the class Amphibia. There are three living orders of amphibians: the frogs and toads (order Anura, or Salientia), the salamanders and newts (order Urodela, or Caudata), and the caecilians, or limbless amphibians (order Gymnophiona, or Apoda), a little known tropical group. Amphibians, the most primitive of the terrestrial vertebrates, are intermediate in evolutionary position between the fish and the reptiles.
Typically amphibians undergo a metamorphosis from an aquatic, water-breathing, limbless larva (called a tadpole) to a terrestrial or partly terrestrial, air-breathing, four-legged adult. The eggs are usually deposited in water or in a protected place where their moisture will be conserved; they have neither shells nor the sets of membranes that surround the eggs of reptiles and other higher vertebrates. Some amphibians lay their eggs in dry places, and the young undergo the larval stage within the egg, emerging as small adults; in these the eggs have evolved various protective structures. Adult amphibians differ from reptiles in having moist skins, without scales or with small, hidden scales.
All living amphibians are specialized for their way of life, none representing the main amphibian stock from which the reptiles evolved. The salamanders and newts are superficially the most similar to ancestral amphibians, having long tails and front and hind legs of approximately equal size. Frogs and toads are highly modified for jumping, with large, muscular hind legs and no tails, while the caecilians have lost all external traces of limbs.
R. Carroll, The Rise of Amphibians (2009).
a combat or transport motor vehicle that can move on land and on water (tank, carrier, automobile, airplane). (1) The amphibious tank and carrier can float because the hermetically sealed body displaces the necessary amount of water. It has a propeller engine, standard caterpillar treads (if it is a caterpillar vehicle), and water jets. The first amphibious tanks were designed during World War I. In 1921—22 amphibious tanks were produced in France and in America. In 1932 the Red Army was supplied with its first amphibious tank, the T-37, which was later replaced by the T-38 and T-40 (1940). The T-40 tank weighs 5.5 tons and has a two-man crew, two machine guns, bulletproof armored plate, and a maximum speed of 44 km an hour on land and 5 km an hour in water.
During World War II, in 1943–45, the US Army used amphibious tanks in several landing operations in the Pacific Ocean and in Europe. But they were of little use for combat actions of ground troops and were used chiefly to provide fire support for landings. In the postwar period many armies began using amphibious tanks, armored carriers, and armored cars on a large scale. At present the term amphibians is rarely applied to these vehicles.
L. G. BARKHUDAROV
(2) The amphibious automobile is used to transport people or freight and to ferry them across rivers, lakes, and other water barriers. It is manufactured on the basis of a crosscountry automobile with all-axle drive. It may have two, three, or four chassis axles. The amphibious automobile has all the units of an ordinary automobile, plus a hermetically sealed body in the shape of a boat or a pontoon for moving on water, a water engine (usually a propeller), a water steering wheel, splash panel, and water pump. The speed of the amphibious automobile on water is 15–20 km an hour.
(3) An amphibious airplane is an aquaplane in the shape of a flying boat that can also come down on land by means of wheels that are lowered.
(4) An amphibious aerosleigh has, instead of skis, a combination float and ski for movement not only on snow, but also on water, on ice with water holes and the like.
A. A. MILUSHKIN