Exoskeleton is absent in class-Amphibia. Some amphibians are with concealed dermal scales. (i) Exoskeleton in reptiles is of horny epidermal scales, shields, plates and scutes. (ii) In Aves, the exoskeleton is epidermal and horny, represented by feathers, scales, claws and sheaths. (iii) The exoskeleton in mammals includes lifeless, horny, epidermal hairs, spines, scales, claws, nail, hoofs, etc. (iv) Fish exoskeleton is of dermal scales, denticles or bony plates covering body surface.