Pronunciation: ex-o-SKEL-e-tun

Etymology: Exoskeleton is derived from two Greek roots that mean outside (exo-, έξω) and fabric (skeletos, σκελετός). The reference is to the material on the outside of the animal.

A hardened outer covering that is secreted by the epidermis. An exoskeleton made of chitin is characteristic of arthropods. However, other hard, external supports like those of the calcareous sponges and the dermal bone coverings of extinct fishes are called exoskeletons.

The photograph below illustrates the components of the exoskeleton of a crayfish, an arthropod.

By Jack R. Holt. Last revised: 01/02/2009