Describe the class Amphibia.

(N/A) As the name indicates (Gr.,Amphi : dual,bios : life),amphibians can live in aquatic as well as terrestrial habitats.
$\rightarrow$ Most of them have two pairs of limbs.
$\rightarrow$ The body is divisible into head and trunk.
$\rightarrow$ $A$ tail may be present in some.
$\rightarrow$ The amphibian skin is moist (without scales).
$\rightarrow$ The eyes have eyelids.
$\rightarrow$ $A$ tympanum represents the ear.
$\rightarrow$ The alimentary canal,urinary and reproductive tracts open into a common chamber called the cloaca,which opens to the exterior.
$\rightarrow$ Respiration is by gills,lungs,and through the skin.
$\rightarrow$ The heart is three-chambered (two auricles and one ventricle).
$\rightarrow$ These are cold-blooded (poikilothermic) animals.
$\rightarrow$ Sexes are separate.
$\rightarrow$ Fertilization is external. They are oviparous and development is indirect.