Write the characteristics of class $Reptilia$.

(N/A) $\rightarrow$ The class name refers to their creeping or crawling mode of locomotion (Latin,$repere$ or $reptum$,to creep or crawl).
$\rightarrow$ They are mostly terrestrial animals and their body is covered by dry and cornified skin,epidermal scales or scutes.
$\rightarrow$ They do not have external ear openings. $Tympanum$ represents the ear.
$\rightarrow$ Limbs,when present,are two pairs.
$\rightarrow$ Heart is usually three-chambered,but four-chambered in crocodiles.
$\rightarrow$ Reptiles are poikilotherms (cold-blooded).
$\rightarrow$ Snakes and lizards shed their scales as skin cast.
$\rightarrow$ Sexes are separate (dioecious).
$\rightarrow$ Fertilisation is internal.
$\rightarrow$ They are oviparous and development is direct.
$\rightarrow$ Examples: $Chelone$ (Turtle),$Testudo$ (Tortoise),$Chameleon$ (Tree lizard),$Calotes$ (Garden lizard),$Crocodilus$ (Crocodile),$Alligator$ (Alligator),$Hemidactylus$ (Wall lizard),Poisonous snakes - $Naja$ (Cobra),$Bangarus$ (Krait),$Vipera$ (Viper).