thumb|upright=1.2|The [[jumping spider Phidippus audax. The basal parts of the chelicerae are the two iridescent green mouthparts.]]
The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated fangs, or as a type of pincers. Some chelicerae, such as those found on nearly all spiders, are hollow and contain (or are connected to) venom glands, used to inject venom into prey or a perceived threat. Both pseudoscorpions and harvestmen—neither of which have that venom channel—have additional structures on their chelicerae that are used for grooming (papillae in pseudoscorpions, cheliceral teeth in Opiliones). In many spider species, males and females have sexually dimorphic chelicerae.
Types
thumb|Types of chelicerae:() jackknife,() scissor,() three-segmented chelate
thumb|Life restoration of the Cambrian [[Megachelicerax, the oldest known chelicerate-bearing arthropod, which has 3-segmented chelicerae]]
Chelicerae can be divided into three kinds: jackknife chelicerae, scissor chelicerae, and three-segmented chelate (pincer-like) chelicerae.
Jackknife chelicerae
The jackknife chelicera is subchelate (with fixed finger much reduced or absent) and is composed of two segments. This type of chelicera occurs exclusively in the Tetrapulmonata.
Jackknife chelicera are described in two different forms: orthognathous and labidognathous. Orthognathous chelicerae are articulated in a manner that enables movements of the appendages parallel to the body axis. This kind of chelicera occurs in the Liphistiomorphae and Mygalomorphae spiders and in the related orders Amblypygi, Schizomida and Uropygi. Labidognathous chelicerae move at right angles to the body axis. This kind of chelicera is rotated and occurs exclusively in the Araneomorphae spiders.
Spider chelicerae
thumb|left|upright|thumb|upright=0.9|3D view of the chelicerae of a [[jumping spider. The pedipalps were removed to see the chelicerae.]]
The chelicerae consist of a base segment, sometimes called the "paturon", that articulates with the cephalothorax (or prosoma) and a fang portion that articulates with the base segment. Such control permits a spider to administer either a dry bite, a dose appropriate to the nature of the prey or enemy, or a maximal dose. (e.g., brown recluse, cellar spider, and crevice weaving spider).
Three-segmented chelate chelicerae
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Limulus polyphemus 201780311 (cropped).jpg|Three-segmented chelicerae of an Atlantic horseshoe crab
Pantopsalis albipalpis 1276804.jpg| Pantopsalis albipalpis, a species of harvestman with exceptionally long three-segmented chelicerae
Acutiramus cummingsi (YPM IP 018609).jpg|Isolated fossil chelicera of a pterygotid eurypterid, Acutiramus cummingsi
</gallery>
Having three-segmented chelate chelicerae is the primitive condition and occurs in arachnids such as the Scorpiones and the Opiliones, as well as in non-arachnid Chelicerata such as the Xiphosura and Eurypterida. The chelifores of the Pycnogonida may be homologous to chelicerae.