Characteristics of Class Reptilia are given below:
1) Class reptilian (L. Reptilia= creeping) includes animals which are cold blooded.
2) The skin has a few cutaneous glands and high levels of keratin, which prevents water loss through the skin.
3) The scales and scutes are formed from the epidermis and are also made of keratin, to protect the body.
4) Reptiles are considered as tetra pods with two sets of paired limbs. Most of these animals have five clawed toes on each limb.
5) All reptiles have spinal columns and a strong skeletal system with a rib cage. They have a well-developed brain and a central nervous system.
6) Unlike amphibians, reptiles do not pass through an embryonic stage with gills. These animals breath with well-developed lungs, right from birth. Most of them have two lungs, except some snakes.
7) All reptiles have three-chambered hearts, except crocodiles, which have four-chambered hearts (2 atria, 2 ventricles), like mammals and birds.
8) Reptiles have a digestive system which has a muscular opening at the base of the tail.
9) In case of reptiles inhabiting arid regions, water is further absorbed into the body and only the remaining waste is excreted.
10) Twelve pairs of cranial nerve.
11) These amniotic eggs can survive without water, as they have protective shells and membranes that allow oxygen and other gases to enter.
12) Respiration by lungs only.
13) The offspring of reptiles resemble the adults at the time of birth itself. There is no metamorphosis, as in the case of amphibians.
14) Lateral sense organs are absent.
15) They are the first animals with amniotic eggs, that can be laid on land and not in water.
16) Reptile's characteristics include internal fertilization, as sperm gets deposited into the reproductive tract of the female directly.
17) The cloaca is present.