Amphibian, one of a large class of cold-blooded vertebrates (animals with backbones). The name comes from Greek words meaning dual life, because most amphibians spend the early part of their life cycle in water and the later part on land. Amphibians include frogs, toads, and salamanders.
Amphibians include caecilians, salamanders, and toads.
There are nearly 2,500 living species of amphibians. They are widely distributed over the world, mostly in freshwater or moist places. A few kinds of toads live in deserts. The smallest amphibian, the oak toad, is 34 inch to 1 14 inches (2 to 3 cm) long; the largest, the giant salamander, reaches 5 12 feet (1.7 m).
Amphibians respire (take in oxygen and let out carbon dioxide) through the skin. They also have other organs of respiration, including gills in the young of all species and the adults of some species, and lungs in the adults of many species. Some amphibians can also respire through the mucous membranes of the mouth.
Most amphibians lay their eggs in water, where they hatch as larvae and develop into adults through a process called metamorphosis. Some amphibian larvae eat only live water animals, such as small insects, mollusks, crustaceans, and worms. Others feed on algae or dead animal matter. Adult amphibians may eat live water animals, or even small birds and mammals. Some amphibians can regrow lost tails or legs during the larval stage, and some even shortly after metamorphosis.
Amphibians make up the class Amphibia. Orders of the class are:
1. Apodathe caecilians. Limbless, wormlike; found in the tropics.
2. Urodelasalamanders, including newts, mud puppies, hellbenders, and axolotls. Tailed; fourlegged.
3. Anuraincludes toads and frogs. Tailless; fourlegged; hind legs adapted for jumping.
There is a type of an amphibian that looks like a worm. Its called a caecilian. Caecilians dont have legs as other amphibians do. However, its really their segmented skin that makes them look like worms.
These creatures, which primarily burrow underground and are hard to find, are different from other amphibians in more ways, too. Their eyes are beneath their skin, and many caecilians have tiny scales embedded in their skin. But they do go through a small metamorphosis. Young caecilians have gills, and adults do not.
Caecilians live only in the tropics. Some can be as long as 5 feet (1.5 meters). Others can be as small as 4 1?2 inches (11.4 centimeters).
Frog populations have been declining since the 1980s. Salamander populations are down, too. No one knows exactly why the numbers of these animals are declining, but its probably the result of many factors.
Because the ozone layer of the atmosphere has thinned, more ultraviolet radiation makes its way to Earth than once did. Frogs eggs dont hatch when exposed to too much radiation.
Pesticides used in farming kill the animals that amphibians eat and may be harmful to amphibians, too. Many of these chemical pollutants drain into water where amphibians can soak them up.
Amphibians live in marshy areas and wetlands. Many of these have been drained for farmland, housing developments, or corporate office parks. Restored wetlands can do a lot to help amphibians survive.
Axolotl, a Mexican salamander that retains most of its larval characteristics, but which matures sexually and is able to reproduce. This ability to reproduce without attaining adult form is called neoteny. Axolotls were first known in the lakes around Mexico City, and were given their name by the Aztecs. They look like the larvae of the tiger salamander, a closely related species. Axolotls are sold in Mexican markets as food.
Neotenic tiger salamanders, often confused with axolotls, are occasionally found in Texas, Kansas, and Oklahoma, and in the Rocky Mountains. In most parts of the United States, however, the tiger salamander attains adult form.
The axolotl is Ambystoma mexicanum; the tiger salamander is A. tigrinum. Both belong to the family Ambystomatidae.
Frog, a small tailless amphibian. Scientifically, there is no distinction between frogs and toads. Both belong to the same order of the class Amphibia, and are collectively called anurans. Popularly, anurans that live in or near freshwater are usually called frogs. They vary in size from certain South American frogs less than one-half inch (13 mm) long to the 10-inch (25-cm) goliath frog of Africa.
Most frogs are green or greenish brown, with various markings in darker or lighter color; some frogs, however, are brightly colored. The frogs of the United States and Canada are smooth-skinned, but in other parts of the world there are frogs with rough or irregular skins. Many kinds of frogs shed their entire skin periodically.
Frogs have webbed hind feet and most are fast swimmers.
Mud Puppy, a salamander that lives in lakes and rivers in the eastern United States. An adult mud puppy is 8 to 17 inches (20 to 43 cm) long. It is brownish or almost black above, with a dark-spotted, pale underside. The rectangular head and body are flattened. The tail fins are often reddish. Each of the four feet has four toes. Dark-red gills wave like plumes outside the gill openings on the neck.
Mud puppies feed on snails, insects, and worms on the muddy bottom. They are sometimes caught accidentally by fishermen. In the spring the female lays 60 to 70 eggs in shallow water, where they hatch in about seven weeks. The young resemble the parents.
The mud puppy is Necturus maculosus of the family Proteidae.
Newt, a salamander found in or near freshwater in North America, Europe, Asia, and North Africa. Most newts spend part of their lives in water and part on land. Most newts are two to six inches (5 to 15 cm) long. Newts have slender bodies, short legs, and long tails. They are greenish, brownish, or blackish above, and yellowish, orangish, or reddish below. The body is typically striped or spotted. The skin of many species secretes a substance that is toxic to predators. Newts feed on insects, spiders, worms, crustaceans, molluscs, and the eggs and larvae of other amphibians.
Newts have slender bodies, short legs, and long tails.
The female lays as many as 400 eggs on submerged vegetation or submerged rocks. Larvae emerge from the eggs in about five weeks. The larvae of some species change into adults in three or four months. Newts of a few species remain in the larval form their entire lives but can reproduce. The larva of the eastern newt, a species found mostly in the eastern United States, lives on land for one to three years and then returns to the water to change into the adult form. In its larval form the animal is known as the red eft. As an adult it is greenish-brown.
Eastern newts go from plant to plant laying one egg at a time.
The California newt is found mostly along the Pacific coast. The larvae are aquatic. They mature into land-dwelling adults, which return to the water only to breed. The California newt is tan or reddish-brown above and yellowish-orange below.
The great (or northern) crested newt of England is about six inches (15 cm) long. The male has a high, fleshy crest down its back and tail.
Salamander, a tailed amphibian. Salamanders are cold-blooded animals (their temperature changes with that of their surroundings). They have soft skin that is usually moist and must have a humid if not wet environment. Most species are found on land; a few are strictly aquatic. Like other amphibians, salamanders are never found in seawater. Land salamanders are often found under stones and logs. Salamanders are found in North America, Asia, Europe, North Africa, and northern South America.
The salamander is a tailed amphibian with soft, moist skin.
Salamanders of most species have four limbs; members of a few species have only two. Most salamanders are from 3 to 8 inches (7.5 to 20 cm) long. The largest species, the giant salamander, grows to about 5 1/2 feet (1.7 m); the smallest is a Mexican species that measures 1 1/2 inches (4 cm). Some species are brightly colored; others are quite dull.
Salamanders are active mainly at night. They feed primarily on insects, spiders, and worms. All salamanders respire to some extent through their skin. Some may also respire through gills, lungs, or the lining of their mouths. Almost all salamanders lay eggs.
Salamanders are often used in laboratory experiments. In some parts of the world, certain species are eaten. Salamanders are sometimes kept as pets. In ancient times it was believed that salamanders could withstand fire and live in flames.
Kinds of Salamanders
There are about 55 genera of salamanders and more than 300 species, grouped into the following 8 families:
Asiatic land salamanders. These are among the most primitive salamanders. They are found only in eastern Asia.
Giant salamanders. Included in this family are the giant salamander (Megalobatrachus japonicus) of Japan and the hellbender (Cryptobranchus alleganiensis) of North America. The hellbender, which inhabits rivers and streams, can reach a length of more than 25 inches (64 cm).
Mole salamanders. Members of this family are found throughout North America. Included in this family are the marbled salamander of the eastern half of the United States and the axolotl. The marbled salamander (Ambystoma opacum) is black with white or grayish markings; it grows to about 5 inches (13 cm).
Fire salamanders and newts. The fire salamanders arc found in Europe and arc of the genus Salamandra.
Amphiumas. There are only two species, found in the southeastern United States. One species (Amphiuma means) grows up to 36 inches (90 cm), the other (A. tridactylum) to about 40 inches (1 m).
Lungless salamanders. It is the largest family, with 180 species. All but two species are found in the Western Hemisphere; the two exceptions are European. Members of this family are from 1 1/2 to 8 1/2 inches (4 to 22 cm) long. Included in this family is the red-backed salamander (Plethodon cinereus).
The red salamander has no lungs, but breathes through its skin and mouth tissue.
Olm and mud puppies. The olm (Proteus anguinus), found in Croatia and Montenegro, is a white salamander that reaches a length of about 12 inches (30 cm).
Sirens. The three species in this family are also permanently larval forms. They are the only salamanders without hind limbs. All three are aquatic and are found in the eastern United States.
Toad, a small, tailless amphibian. Scientifically, there is no distinction between toads and frogs. Both belong to the same order of the class Amphibia, and are called anurans. However, because of popular usage, zoologists use the term true toads to describe only one family of anurans, the Bufonidae.
Toads have shorter hind legs than frogs, and hop instead of leap.
True toads are found throughout the world, excepting the polar regions, Australia and neighboring islands, and Madagascar. They have shorter hind legs than frogs, and hop instead of leap. Generally, their skin is rougher than that of frogs. Toads vary in length from about 3/4 of an inch (2 cm) to more than 9 inches (23 cm).
Glands in the toad’s skin secrete a fluid that is poisonous to most of the toad’s enemies. Humans are not usually affected by handling toads, but find the secretion of some species irritating to mucous membranes. There is no basis in the belief that toads cause warts. In China, toad skins were used for centuries in the treatment of heart diseases. In modern times, several drugs have been isolated from toad skin secretion. One of these drugs, bufotenine, has a stimulating effect on the heart similar to that of digitalis.
Toad skin is rougher than that of frogs.
The breeding habits and life cycle of toads are almost identical to those of other anurans. (S Toads that live in dry regions do not breed until there is sufficient rainfall to form pools. These pools must be large enough to remain until the larvae, or tadpoles, metamorphose and can live on land. If the pools dry up too soon, the tadpoles die. Some kinds of toads lay their eggs singly, others in masses of thousands.
Tadpoles feed on algae and other water vegetation. Adult toads eat insects, spiders, and worms. The toad’s long tongue, like the frog’s, is fastened toward the front of its mouth, and is darted out swiftly to catch prey. The prey is swallowed whole. Toads feed mostly at night and remain in burrows or moist, shaded spots during the day. In dry regions, toads stay in burrows or bury themselves in the ground during the hottest part of the year, coming out during periods when rain falls.