Editing Chelicerata (section)

===Chelicerae and pedipalps===
Chelicerae and pedipalps are the two pairs of appendages closest to the mouth; they vary widely in form and function and the consistent difference between them is their position in the embryo and corresponding neurons: [[chelicera]]e are deutocerebral and arise from somite 1, ahead of the mouth, while [[pedipalp]]s are tritocerebral and arise from somite 2, behind the mouth.<ref name="RuppertFoxBarnes2004ChelicerataGen" /><ref name=":1" /><ref name=":3" />

The chelicerae ("claw horns") that give the sub-phylum its name normally consist of three sections, and the claw is formed by the third section and a rigid extension of the second.<ref name="RuppertFoxBarnes2004ChelicerataGen" /><ref name="BraddyPoschmannTetlie2008GiantClaw">{{cite journal |author1=Braddy, S.J. |author2=Poschmann, M. Markus |author3=Tetlie, O.E. |name-list-style=amp |title=Giant claw reveals the largest ever arthropod |journal=Biology Letters |year=2008 |volume=4 
|issue=1 |pmid=18029297 |pages=106–109 |pmc=2412931 |doi=10.1098/rsbl.2007.0491 |df=dmy-all}}</ref> However, spiders' have only two sections, and the second forms a fang that folds away behind the first when not in use.<ref name="RuppertFoxBarnes2004Spiders" /> The relative sizes of chelicerae vary widely: those of some fossil [[eurypterid]]s and modern [[harvestmen]] form large claws that extended ahead of the body,<ref name="BraddyPoschmannTetlie2008GiantClaw" /> while [[scorpion]]s' are tiny pincers that are used in feeding and project only slightly in front of the head.<ref name="RuppertFoxBarnes2004Scorpions">{{harvnb|Ruppert|Fox|Barnes|2004|pp=565–569}}</ref>

In basal chelicerates, the pedipalps are unspecialized and subequal to the posterior pairs of walking legs.<ref name=":1" /> However, in sea spider and arachnids, the pedipalps are more or less specialized for sensory<ref name="RuppertFoxBarnes2004ChelicerataGen" /> or prey-catching function<ref name=":1" /> – for example scorpions have pincers<ref name="RuppertFoxBarnes2004Scorpions" /> and male spiders have bulbous tips that act as [[syringe]]s to inject [[sperm]] into the females' reproductive openings when mating.<ref name="RuppertFoxBarnes2004Spiders" />

{{Annotated image | float=right | caption={{{caption|Spider's main organs<ref name="RuppertFoxBarnes2004p571to584">{{cite book 
| author=Ruppert, E. E. | author2=Fox, R. S. | author3=Barnes, R. D. 
| name-list-style=amp | title=Invertebrate Zoology 
| publisher=Brooks / Cole | edition=7th | isbn=0030259827 | date=2004 | pages=571–584
}}</ref>}}} | image=Spider main organs labelled.png | width=350 | image-width=350 | height=520 
| annotations=
{{Annotation|5|260|<span style{{=}}"background-color:blue">&nbsp;&nbsp;&nbsp;</span> Nervous system}}
{{Annotation|175|260|<span style{{=}}"background-color:#207326">&nbsp;&nbsp;&nbsp;</span> Digestive & excretory}}
{{Annotation|191|280|system}}
{{Annotation|5|280|<span style{{=}}"background-color:#b51136">&nbsp;&nbsp;&nbsp;</span> Circulatory system}}
{{Annotation|175|300|<span style{{=}}"background-color:#f5816a">&nbsp;&nbsp;&nbsp;</span> Respiratory system}}
{{Annotation|5|300|<span style{{=}}"background-color:yellow">&nbsp;&nbsp;&nbsp;</span> Reproductive system}}
{{Annotation|5|325|&nbsp;&nbsp;1 [[Chelicera]]}}
{{Annotation|175|325|&nbsp;&nbsp;2 [[Venom]] [[gland]]}}
{{Annotation|5|345|&nbsp;&nbsp;3 [[Brain]]}}
{{Annotation|175|345|&nbsp;&nbsp;4 Pumping [[stomach]]}}
{{Annotation|5|365|&nbsp;&nbsp;5 Forward [[aorta]] branch}}
{{Annotation|175|365|&nbsp;&nbsp;6 Digestive [[cecum]]}}
{{Annotation|5|385|&nbsp;&nbsp;7 [[Heart]]}}
{{Annotation|175|385|&nbsp;&nbsp;8 Midgut}}
{{Annotation|5|405|&nbsp;&nbsp;9 [[Malphigian tubules]]}}
{{Annotation|175|405|10 Stercoral pocket}}
{{Annotation|5|425|11 Rear [[aorta]]}}
{{Annotation|175|425|12 [[Spinneret (spider)|Spinneret]]}}
{{Annotation|5|445|13 [[Silk]] [[gland]]}}
{{Annotation|175|445|14 [[invertebrate trachea|Trachea]]}}
{{Annotation|5|465|15 [[Ovary]] (female)}}
{{Annotation|175|465|16 [[Book lung]]}}
{{Annotation|5|485|17 [[Ventral nerve cord|Nerve cord]]}}
{{Annotation|175|485|18 Legs}}
{{Annotation|5|505|19 [[Pedipalp]]}}
}}