Chelicera

The chelicerae /kəˈlɪsəriː/, are the mouthparts of the Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", some chelicerae, such as those found in spiders, are hollow and contain (or are connected to) venom glands, and are used to inject venom into prey or a (perceived) threat.

Chelicerae can be divided into three kinds: jackknife chelicerae, scissor chelicerae, and 3-segmented chelate 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 presents 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, Thelyphonida. Labidognathous chelicerae moves at right angles to the body axis. This kind of chelicera is rotated and occurs exclusively in the Araneomorphae spiders.

The chelicerae consist of a base segment that articulates with the cephalothorax and a fang portion that articulates with the base segment. All spiders have venom glands and can inject the venom through openings in the tips of their fangs when biting prey. The glands that produce this venom are located in the two segments of the chelicerae, and, in most spiders, extend beyond the chelicerae and into the cephalothorax.

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