Characteristics of reptiles

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Sauropsida

Subclasses: Anapsida Diapsida

Today they are represented by four orders:
Crocodilia (crocodiles, gharials, caimans and alligators): 23 species

Sphenodontia (tuataras from New Zealand): 2 species

Squamata (lizards, snakes and amphisbaenids ("worm-lizards"): approximately 7,900 species
Testudines (turtles and tortoises): approximately 300 species

Characteristics:

Reptiles are cold-blooded (Ectothermic), scaly skinned vertebrates. Skeleton is made of bone. Their hearts have three or (except the crocodiles which have a four-chambered heart), and, like humans, they breathe through lungs. They have claws on their toes (except those which do not have legs, such as legless lizards).

There are a variety of body shapes that help the animal to adapt to its environment. A reptile must adjust its body temperature to its environment .The body of a reptile works optimally when it can get the right amount of heat from its surroundings.
Reproduction

Fertilization is internal: They are the first animals, in evolution, to develop the amniotic egg,as covered by a leathery shell. This allows reptiles to lay eggs on land. They do not have a larval stage.

References:
http://id.essortment.com/reptilessnakes_rhus.htm
http://www.hoover.k12.al.us/hhs/Science/jclopton/HWAssist/reptiles/reptiles%20study%20guide.htm