Describe the characteristics of the first tetrapods (Class Amphibia).

(N/A) $\rightarrow$ As the name indicates (Gr.,Amphi : dual,bios : life),amphibians can live in both aquatic and terrestrial habitats.
$\rightarrow$ Most of them possess two pairs of limbs.
$\rightarrow$ The body is divisible into head and trunk; a tail may be present in some.
$\rightarrow$ The skin is moist and lacks 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 occurs through gills,lungs,and the skin.
$\rightarrow$ The heart is three-chambered (two auricles and one ventricle).
$\rightarrow$ These are cold-blooded (poikilothermic) animals.
$\rightarrow$ Sexes are separate,and fertilization is usually external.