Forcipule

"Poison claw" redirects here. For the poison claw sea urchin, see Toxopneustes pileolus.

Forcipules are the modified, pincer-like, front legs of centipedes that are used to inject venom into prey.^[1][2] They are the only known examples of front legs acting as venom injectors.^[1][3]

Nomenclature

Forcipules go by a variety of names in both scientific and colloquial usages. They are sometimes known as poison claws or jaw legs,^[4] referencing their evolution from maxillipeds, a term which they are also sometimes known by in the context of centipedes (maxillipeds, maxillipedes). Other names include prehensors, telopodites, and forcipulae (singular forcipula).^[5][6] In the specific case in which the forcipules are used to inject venom, they are called toxicognaths (from toxic + the Greek gnathos, jaw).^[7]

The term forcipule references their similarity with forceps.^[1]

Scientific illustration of a forcipule

Anatomy, systematics, and variation

The forcipules of Eupolybothrus cavernicolus (Lithobiidae)

Forcipules evolved from the maxillipeds – front legs – of centipedes' last common ancestor, believed to be somewhat Scutigeromorph-like. They were initially leg-like, then progressed into a more pincer or claw-like shape, as seen today, and restricted to horizontal movement.^[1] The forcipules of modern Scutigeromorphs are the most significantly different in shape: they are more leg-like, and cannot hold prey like they are used among other orders: they are used for envenomation only, making their use more comparable to a knife than a pincer.^[8]