There are certain characters acquired by reptiles for the terrestrial adaptations. Two of then are

(i) Their body is covered by dry and cornified skin and epidermal scales or scutes.

(ii) Fertilisation is internal.

Every living form maintain a proper shape, size and structure. In multicellular lower organisms the shape of body is maintained by certain biological materials like chitin and calcium substances. Chitinous exoskeleton is the characteristic feature of arthropods. (e.g., cockroach, termite,wasp) whereas, calcareous shell is present in molluscs (gastropods). (e.g., snail and slugs).

The phenomenon of production and emission of light by an organism as a result of chemical reaction during which chemical energy is converted to light energy is called bioluminescence.

Ctenoplana from phylum-Ctenophora, exhibits the phenomenon of bioluminescence.

(a) Crocodilus (crocodile) is a cold blooded animal.

(b) Elephas maximus (elephant), (mammal) is warm blooded animal.

(c) Testudo (tortoise) bears dry and cornified skin.

(d) Ascaris (roundworm) is a dioecious animal.

Animals in which the cells are arranged in two embryonic layers, an external ectoderm and an internal endoderm are called diploblastic animals (e.g., coelentrates). While those animals in which the developing embryo has a third germinal layer, i.e., mesoderm lying between the ectoderm and endoderm are called triploblastic animals. (e.g., chordates).