Chelicerae

Definition

The paired, jointed mouthpart appendages characteristic of the subphylum Chelicerata, positioned anterior to the mouth and used in feeding, defense, and grooming. Structurally, chelicerae consist of a basal segment (paturon) and a movable distal segment (fang or claw), operating in a scissor-like or pincer-like fashion. In spiders (Araneae), the fang is typically hollow and connected to venom glands for envenomation; in scorpions, the chelae (pincers) are enlarged pedipalps rather than chelicerae, whose own chelicerae are small and chelate. Harvestmen (Opiliones) and pseudoscorpiones possess chelate chelicerae with grooming organs (rallum) but lack venom apparatus. Sea spiders (Pycnogonida) and horseshoe crabs (Xiphosura) bear simpler, unjointed or weakly jointed chelicerae. Chelicerae are homologous to the antennae of mandibulate arthropods and represent a defining synapomorphy of the chelicerate lineage.

Etymology

From Greek chele (claw, pincer) + keras (horn), referring to the claw-like structure.

Example

In a wandering spider (Cupiennius), the chelicerae project downward from the cephalothorax; when striking prey, the fang pivots from the paturon to penetrate the cuticle, while muscular compression of the venom gland forces neurotoxic venom through the hollow fang canal.

Synonyms

• jaws (informal)

Related Terms

• Chelicerata
• pedipalp
• fang
• paturon
• rallum
• subchelate
• Cephalothorax
• venom gland
• Arachnida
• Xiphosura

Usage Notes

The term is plural; singular is rarely used in practice. Specialists distinguish chelicerae from mandibles: chelicerae are the only preoral appendages in Chelicerata and are not homologous to the mandibles of insects and crustaceans. Sexual dimorphism in chelicerae is well-documented in many spider families, with males often bearing enlarged or modified structures used in mating displays or combat. In scorpions, the large pincers are pedipalps, not chelicerae—a common point of confusion. The adjectival form is cheliceral.