Chelicerae

The chelicerae (/kəˈlɪsəriː/) are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders.

This kind of chelicera occurs in the Liphistiomorphae and Mygalomorphae spiders and in the related orders Amblypygi, Schizomida and Uropygi.

[2] The control is also necessary for actions such as the spitting of venomous silk by members of the family Scytodidae; they depend on that mechanism both in hunting and defence.

When a spider bites, the two parts of the chelicerae come together like a folding knife, and when making a threat display or actually preparing to bite, the spider will open the angle of the fangs with the basal portion of the chelicerae and also open the angle of the basal portion with the cephalothorax.

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 jumping spider Phidippus audax . The basal parts of the chelicerae are the two iridescent green mouthparts.
Types of chelicerae: (A) jackknife, (B) scissor, and (C) 3-segmented chelate
3D view of the chelicerae of a jumping spider . The pedipalps were removed to see the chelicerae.
Spider chelicerae. The chelicerae are shown in black, the surface of the cephalothorax in brown, the legs in reddish brown, and the venom glands and surrounding muscle tissue in green. The fang portion of the right chelicera can be seen projecting into the space between the two chelicerae.