Chelicerae
The chelicerae (
Types
Chelicerae can be divided into three kinds: jackknife chelicerae, scissor chelicerae, and 3-segmented chelate chelicerae.[2]
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.[3]
Spider chelicerae
The chelicerae consist of a base segment, sometimes called the "paturon", that articulates with the
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.[2] 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.[2] 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
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Uncate chelicerae of a solifuge
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Front view of a brown recluse spider, showing its chelicerae
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Uncate chelicerae of a pseudoscorpion
The uncate chelicera is chelate and composed of two segments and occurs in the orders
3-segmented chelate chelicerae
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3-segmented chelicerae of an Atlantic horseshoe crab
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Pantopsalis albipalpis, a species of harvestman with exceptionally long 3-segmented chelicerae
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Isolated fossil chelicera of apterygotid eurypterid, Acutiramus cummingsi
This is the primitive condition and occurs in
References
- PMID 22410577. Retrieved 5 September 2020.
- ^ ISBN 0-19-509594-4.
- ^ Zonstein, S. L. (2004). D. V. Logunov & D. Penney (ed.). "The spider chelicerae: some problems of origin and evolution" (PDF). Arthropoda Selecta (Special Issue no. 1: European Arachnology 2003): 349–366. Archived from the original (PDF) on 2017-10-10. Retrieved 2017-05-02.
- ISBN 978-0-8014-7985-4. Retrieved 1 January 2020.
External links
- Media related to Chelicerae at Wikimedia Commons