A chaeta or cheta (see spelling differences) is a chitinous bristle or seta found on an insect, arthropod or annelid worms such as the earthworm, although the term is also frequently used to describe similar structures in other invertebrates. The plural form is chaetae or chetae.In the Polychaeta, they are located on the parapodia.A range of chaetal shapes and formats exists. Particular forms of chaetae are often species-specific, giving the features a useful taxonomic function.