Chaetae

Definition

Bristle-like, often chitinous cuticular outgrowths projecting from the body wall of invertebrates, particularly segmented worms (Annelida) and arthropods. In arthropods, chaetae are typically solid, non-articulated filaments secreted by single epidermal cells, distinct from the jointed, hollow setae that are more common in insects and arachnids. They serve sensory, defensive, locomotory, or secretory functions depending on position and morphology.

Etymology

From Greek 'khaitē' meaning long flowing hair or mane.

Example

Polychaete annelids bear dense bundles of chaetae on each parapodial lobe that anchor the worm during burrowing; some beetle larvae possess caudal chaetae that aid in locomotion through soil.

Synonyms

• bristles

Related Terms

• setae
• spines
• trichobothria
• Cuticle
• Parapodium
• sensilla
• macrochaetae
• microchaetae

Usage Notes

In arthropod literature, 'chaetae' and 'setae' are sometimes treated as synonyms, but specialists increasingly restrict 'chaetae' to the solid, non-articulated bristles of annelids and certain basal arthropods (e.g., Onychophora, some crustaceans), while reserving 'setae' for the hollow, articulated hairs typical of insects and arachnids. The plural 'chaetae' is standard in scientific writing; 'chaetas' is archaic. Macrochaetae and microchaetae refer to size classes, particularly in dipteran chaetotaxy.