What are amphibians?
Amphibians form a Class of Vertebrates (other Classes include reptiles, birds and mammals) with over 4000 species worldwide. They have no unique structure, like the feathers of birds, which sets them apart from all other animals. There are a few characteristics which all amphibians share:
They are ectotherms (often referred to as cold-blooded). This means that amphibians do not hold their body temperature constant like mammals, but their internal temperature depends upon that of the surrounding environment.
Amphibians have soft, generally moist skin without scales.
The eggs do not have shells and so must be laid in water or a damp environment to keep from drying out.
Amphibians go through a two-stage life cycle. When an amphibian hatches it is in a gilled larval form. In frogs and toads this larva is called a tadpole. After a few weeks or months the larvae transform into the adult form of a frog or salamander, however it may still take a few years to become mature.
How many kinds of amphibians are there?
Biologists divide amphibians into three major groups or Orders. Two of these, the Frogs (including toads) and the Salamanders are found in Canada. The third group is the Caecilians -- limbless amphibians found only in the tropics.