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.