Editing Chelicerae (section)

==Types==
[[File:Chelicerae.svg|thumb|Types of chelicerae: (A) jackknife, (B) scissor, and (C) 3-segmented chelate]]
[[File:Jumping spider fang 3D.jpg|thumb|upright=0.9|3D view of the chelicerae of a [[jumping spider]]. The [[pedipalp]]s were removed to see the chelicerae.]]
Chelicerae can be divided into three kinds: jackknife chelicerae, scissor chelicerae, and three-segmented [[wikt:chelate|chelate]] chelicerae.<ref name="Foelix"/>

===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 [[Mesothelae|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.<ref>{{cite journal |first=S. L. |last=Zonstein |year=2004 |title=The spider chelicerae: some problems of origin and evolution |editor=D. V. Logunov & D. Penney |journal=[[Arthropoda Selecta]] |issue=Special Issue no. 1: European Arachnology 2003 |pages=349–366 |url=http://www.european-arachnology.org/wdp/wp-content/uploads/2015/08/349_366_Zonstein.pdf |access-date=2017-05-02 |archive-date=2017-10-10 |archive-url=https://web.archive.org/web/20171010160051/http://www.european-arachnology.org/wdp/wp-content/uploads/2015/08/349_366_Zonstein.pdf |url-status=dead }}</ref>

====Spider chelicerae====
[[File:Spider chelicerae.png|thumb|left|upright|{{center|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.}}]]
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.<ref name="Foelix"/> Almost all spiders have venom glands and can inject the venom through openings near the tips of their fangs when [[spider bite|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.<ref name="Foelix"/> The fang, the organic functional equivalent to a [[hypodermic needle]] is what penetrates the skin, fur, or exoskeleton of the spider's target—spider mouthparts are primarily intended for envenoming a spider's prey in most species, typically [[insect]]s and other small [[arthropod]]s.<ref name="Foelix"/> The basal portion includes all or part of the spider's venom glands, which can be squeezed to control the amount of venom forced out of the glands.<ref name="Foelix">{{cite book |author=Rainer F. Foelix |title=Biology of Spiders |edition=2nd |publisher=[[Oxford University Press]] |isbn=0-19-509594-4 |year=1996 |url-access=registration |url=https://archive.org/details/biologyofspiders00foel_0 }}</ref> 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.<ref name="Foelix"/> The control is also necessary for actions such as the spitting of venomous silk by members of the family [[Spitting spider|Scytodidae]]; they depend on that mechanism both in hunting and defence.

{{Multiple image
| direction = horizontal
| align = center
| caption_align = center
| header = Chelicerae of ''[[Psalmopoeus cambridgei]]''
| image1 = Psalmopoeus cambridgei Fang 60x.jpg
| width1 = 200
| caption1 = The fang is about 2mm long. The spider itself is about 25mm long.
| image2 = Psalmopoeus cambridgei Fang and hypo.jpg
| width2 = 190
| caption2 = Microphotograph of the same chelicera and the tip of a 22–gauge ({{convert|0.025|in|mm|abbr=on|order=flip}}) hypodermic needle
}}

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.<ref name="Foelix"/> In the tarantulas and other [[Mygalomorphae]], the horizontal separation of the tips of the fangs does not change much, but in the other spiders the tips of the fangs move apart from each other as well as elevating.<ref name="Foelix"/> Even the tips of the fangs of the rather large spider shown above are quite sharp, and the spider's body is well adapted to driving the fangs into flesh. Some spider bites, such as those of the [[Sydney funnel-web spider]], are reported to have penetrated toenails and soft leather shoes.

===Uncate chelicerae===
<gallery mode="packed">
850 8879 Solifugae.jpg|Uncate chelicerae of a solifuge
Anterior view of Loxosceles reclusa (Brown Recluse Spider) (22830337766).jpg| Front view of a brown recluse spider, showing its chelicerae
Pseudoscorpion (7586033338).jpg|Uncate chelicerae of a pseudoscorpion
</gallery>
The uncate chelicera is chelate and composed of two segments and occurs in the orders [[Pseudoscorpiones]], [[Solifugae]], [[Ricinulei]], and [[Spider|Araneae]]<ref>{{cite book |last1=Vetter |first1=Richard S. |title=The Brown Recluse Spider |date=2015 |publisher=Cornell University Press |location=Ithaca, New York |isbn=978-0-8014-7985-4 |page=19 |edition=1st |url=https://www.cornellpress.cornell.edu/book/9780801479854/the-brown-recluse-spider/#bookTabs=1 |access-date=1 January 2020}}</ref> (e.g., [[brown recluse spider|brown recluse]], [[Pholcidae|cellar spider]], and [[Crevice weaver|crevice weaving spider]]).

===Three-segmented chelate chelicerae===
<gallery mode="packed">
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|Acutiramus cummingsi]]''
</gallery>
Having three-segmented chelate chelicerae is the primitive condition and occurs in [[arachnid]]s such as the [[Scorpion]]es and the [[Opiliones]], as well as in non-arachnid Chelicerata such as the [[Xiphosura]] and [[Eurypterida]].<ref>{{cite journal |last1=Schmidt |first1=Michel |last2=Melzer |first2=Roland R. |title=The "elongate chelicera problem": A virtual approach in an extinct pterygotid sea scorpion from a 3D kinematic point of view |journal=Ecology and Evolution |date=May 2024 |volume=14 |issue=5 |pages=e11303 |doi=10.1002/ece3.11303 |pmid=38766312 |language=en |issn=2045-7758|pmc=11099745 }}</ref> The chelifores of the [[Pycnogonida]] may be homologous to chelicerae.<ref>{{cite journal |last1=Nakamura |first1=Koichiro |last2=Kano |first2=Yasunori |last3=Suzuki |first3=Nobuo |last4=Namatame |first4=Takashi |last5=Kosaku |first5=Akinori |title=18S rRNA phylogeny of sea spiders with emphasis on the position of Rhynchothoracidae |journal=Marine Biology |date=1 December 2007 |volume=153 |issue=2 |pages=213–223 |doi=10.1007/s00227-007-0803-0 |url=https://link.springer.com/article/10.1007/s00227-007-0803-0 |language=en |issn=1432-1793|url-access=subscription }}</ref>