amphibian

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amphibian,

in zoology, cold-blooded vertebratevertebrate,
any animal having a backbone or spinal column. Verbrates can be traced back to the Silurian period. In the adults of nearly all forms the backbone consists of a series of vertebrae. All vertebrates belong to the subphylum Vertebrata of the phylum Chordata.
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 animal of the class Amphibia. There are three living orders of amphibians: the frogsfrog,
common name for an amphibian of the order Anura. Frogs are found all over the world, except in Antarctica. They require moisture and usually live in quiet freshwater or in the woods. Some frogs are highly aquatic, while others are better adapted to terrestrial habitats.
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 and toadstoad,
name applied to certain members of the amphibian order Anura, which also includes the frog. Although there is no clear-cut distinction between toads and frogs, the name toad
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 (order Anura, or Salientia), the salamanderssalamander,
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
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 and newtsnewt,
name for members of a large salamander family, widely distributed in the Northern Hemisphere and including the common European salamanders. Newts are lizardlike in shape and are usually under 6 in. (15 cm) long including the slender tail.
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 (order Urodela, or Caudata), and the caecilianscaecilian
, any of the legless, tailless tropical amphibians belonging to the order Gymnophiona (or Apoda). Most adult caecilians resemble earthworms superficially but have vertebrate characteristics such as jaws and teeth.

Caecilians range in size from 7 in. to 4.
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, 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 fishfish,
limbless aquatic vertebrate animal with fins and internal gills. Traditionally the living fish have been divided into three class: the primitive jawless fishes, or Agnatha; the cartilaginous (sharklike) fishes, or Chondrichthyes; and the bony fishes, or Osteichthyes.
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 and the reptilesreptile,
name for the dry-skinned, usually scaly, cold-blooded vertebrates (see Chordata) of the order Reptilia. Reptiles are found in a variety of habitats throughout the warm and temperate regions (except on some islands), with the greatest variety in the tropics.
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.

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.

Bibliography

R. Carroll, The Rise of Amphibians (2009).


amphibian,

in aviation: see seaplaneseaplane,
airplane designed to take off from and alight on water. The two most common types are the floatplane, whose fuselage is supported by struts attached to two or more pontoon floats, and the flying boat, whose boat-hull fuselage is constructed with the buoyancy and
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.

Amphibian

 

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

amphibian

1. any cold-blooded vertebrate of the class Amphibia, typically living on land but breeding in water. Their aquatic larvae (tadpoles) undergo metamorphosis into the adult form. The class includes the newts and salamanders, frogs and toads, and caecilians
2. a type of aircraft able to land and take off from both water and land
3. any vehicle able to travel on both water and land
4. another word for amphibious