WHAT IS AN AMPHIBIAN?
Amphibians are animals that live part of their lives in water and part on land. Amphibians are vertebrates, and are also ectothermic. They cannot regulate their own body heat, so they depend on warmth from sunlight to become warm and active. They also can't cool down on their own, so if they get too hot, they have to find a burrow or some other shade. In cold weather, they tend to be sluggish and do not move around much.
Young amphibians do not look like their parents. They are generally called larvae, and as they develop, they change in body shape, diet, and lifestyle, a process called metamorphosis. A frog is a good example, starting out as a tadpole with gills to breathe underwater and a tail to swim with. As it gets older it then develops lungs, legs, and a different mouth. Its eyes also change position and it loses its tail. At this point it is an adult frog, which spends most of its time hopping on land, rather than swimming like a fish in water.
MOIST IS BEST
Most amphibians have soft, moist skin that is protected by a slippery secretion of mucus. They also tend to live in moist places or near water to keep their bodies from drying out. Many adult amphibians also have poison-producing glands in their skin, which make them taste bad to predators and might even poison a predator that bites or swallows them. Some of these amphibians, like poison dart frogs, are brightly colored as a warning: Don't eat me, or you'll be sorry!
THREE GROUPS OF AMPHIBIANS
There are about 5,500 known species of amphibians, divided into 3 main groups: salamanders, newts, and mudpuppies; caecilians; and frogs and toads. The largest amphibian is the Japanese giant salamander Andrias japonicus, at 6 feet long (1.8 meters) and 140 pounds (63 kilograms), and the smallest is a poison dart frog Psyllophryne didactyla that is only 0.5 inches long (1.3 centimeters) and weighs just under 1 ounce (28 grams).