Exoskeleton

An Exoskeleton is an external alternative to the skeleton of most vertebrates. All arthropods (insects, arachnids and crustaceans) have exoskeletons as do many other invertebrates and some species with internal skeletal structures also sport exoskeletons.

Like a skeleton exoskeletons support the body but also often work as a from of armour.

Most (is not all) Insectoid species feature exoskeletons, as do the Ascendants, the Tholians and the Lirin (DS9 novel: Rising Son, ENT episode: In a Mirror, Darkly & EV comic: Our Dearest Blood). The Lirin exoskeleton is composed of Chitin (EV comic: Our Dearest Blood). Borg drones also feature Exo-plating which carries out a similar armour function to exoskeletons.