Chelicera

Definition

The first pair of appendages flanking the mouth in chelicerate arthropods, serving as jaws or feeding structures. Chelicerae are typically segmented and may be modified into fangs (as in spiders), pincers (as in pseudoscorpions), or shearing blades (as in horseshoe crabs and solifuges). Unlike the mandibles of insects and crustaceans, chelicerae lack a palp and operate in the sagittal plane. They are diagnostic for the subphylum Chelicerata and exhibit considerable functional diversity correlated with diet and predatory strategy.

Etymology

From Greek chelē 'claw' + keras 'horn', referring to the pincer-like or horned appearance of these appendages.

Example

In wandering spiders (Ctenidae), the chelicerae bear a pair of massive, vertically articulated fangs with associated venom glands; when at rest, the fangs fold back against the chelicerae, then swing down to strike prey.

Synonyms

• cheliceral appendage

Related Terms

• pedipalp
• Mandible
• Maxilla
• subchelate
• fang
• Chelicerata
• prosoma
• venom gland

Usage Notes

Chelicerae are homologous across Chelicerata but highly divergent in form: arachnologists distinguish between 'jackknife' chelicerae (two-segmented, folding) in Araneae and Opiliones versus 'scissor' chelicerae (three-segmented, lateral) in Pseudoscorpiones. The term is sometimes misspelled 'cheliceræ' or confused with 'chela' (the pincer of a crustacean claw). Sexual dimorphism in chelicera size or armature is common in spiders and harvestmen.