An elytron (from Greek: ἔλυτρον ; plural: elytra) is a modified, hardened forewing of certain insect orders, notably beetles (Coleoptera) and a few of the true bugs (Heteroptera); in most true bugs, the forewings are instead called hemelytra, as only the basal half is thickened while the apex is membranous. An elytron is sometimes also referred to as a shard.
The elytra primarily serve as protective wing-cases for the hindwings underneath, which are used for flying. To fly, a beetle typically opens the elytra and then extends the hindwings, flying while still holding the elytra open, though some beetles in the families Scarabaeidae and Buprestidae can fly with the elytra closed.
In some groups, the elytra are fused together, rendering the insect flightless. Some of the ground beetles (family Carabidae) are a good example of this.
The term is also used to describe the hard scales of some polychaete worms, notably the Polynoidae. These outgrowths of the body wall are distinguished from chaeta, which grow from follicles and thus possess roots.