Editing Arachnid (section)

{{Short description|Class of arthropods}}
{{Other uses}}
{{Redirect|Arachnida|the arachnida curve|Sectrix of Maclaurin}}
{{Automatic taxobox
| fossil_range = {{Fossil range|435|0}}<small>[[Llandovery epoch|Early Silurian]] – [[Holocene|present]]</small>
| image = <imagemap>
File:Arachnida collage.png|300px|center
rect 1 1 400 300 [[Spider|Araneae]]
rect 400 1 800 300 [[Amblypygi]]
rect 800 1 1200 300 [[Uropygi]]

rect 1 300 400 600 [[Schizomida]]
rect 400 300 800 600 [[Scorpion]]es
rect 800 300 1200 600 [[Pseudoscorpion]]es

rect 1 600 400 900 [[Solifugae]]
rect 400 600 800 900 [[Ricinulei]]
rect 800 600 1200 900 [[Opiliones]]

rect 1 900 400 1200 [[Palpigradi]]
rect 400 900 800 1200 [[Acariformes]]
rect 800 900 1200 1200 [[Parasitiformes]]
</imagemap>
| image_upright = 1.3
| image_caption = Representatives of the 12 extant orders of arachnids
| display_parents = 2
| taxon = Arachnida
| authority = [[Lamarck]], 1801
| subdivision_ranks = Subdivisions
| subdivision = * [[Solifugae]]&nbsp;– camel spiders
* [[Opiliones]]&nbsp;– harvestmen
* [[Ricinulei]]&nbsp;- "hooded tickspiders"
* [[Acari]] (likely polyphyletic)
** [[Acariformes]]&nbsp;– various mites
** [[Parasitiformes]]&nbsp;– various mites and ticks
* †[[Phalangiotarbida]] 
* [[Palpigradi]]&nbsp;– micro-whipscorpions
* [[Arachnopulmonata]]
** [[Panscorpiones]]<ref>{{Cite journal |last1=Gainett |first1=Guilherme |last2=Klementz |first2=Benjamin C. |last3=Setton |first3=Emily V. W. |last4=Simian |first4=Catalina |last5=Iuri |first5=Hernán A. |last6=Edgecombe |first6=Gregory D. |last7=Peretti |first7=Alfredo V. |last8=Sharma |first8=Prashant P. |date=July 2024 |title=A plurality of morphological characters need not equate with phylogenetic accuracy: A rare genomic change refutes the placement of Solifugae and Pseudoscorpiones in Haplocnemata |url=https://onlinelibrary.wiley.com/doi/10.1111/ede.12467 |journal=Evolution & Development |language=en |volume=26 |issue=4 |pages=e12467 |doi=10.1111/ede.12467 |pmid=38124251 |issn=1520-541X|hdl=11086/552527 |hdl-access=free }}</ref>
*** [[Scorpion]]es&nbsp;– scorpions
*** [[Pseudoscorpion]]es&nbsp;– pseudoscorpions
** Pantetrapulmonata
*** †''[[Douglassarachne]]''
***[[Ricinulei]]?
***†[[Trigonotarbida]] 
*** [[Tetrapulmonata]]
**** †''[[Xenarachne]]''
**** [[Schizotarsata]]
***** †[[Haptopoda]] 
***** [[Pedipalpi]]
****** [[Amblypygi]]&nbsp;– whip spiders
****** [[Schizomida]]&nbsp;– short-tailed whipscorpions
****** [[Uropygi]]&nbsp;– vinegaroons
**** [[Serikodiastida]]
***** †''[[Idmonarachne]]''
***** †[[Uraraneida]] 
***** [[Spider|Araneae]]&nbsp;– spiders
}}
'''Arachnids''' are [[arthropod]]s in the [[Class (biology)|class]] '''Arachnida''' ({{IPAc-en|ə|ˈ|r|æ|k|n|ɪ|d|ə}}) of the subphylum [[Chelicerata]]. Arachnida includes, among others, [[spider]]s, [[scorpion]]s, [[tick]]s, [[mite]]s, [[pseudoscorpion]]s, [[opiliones|harvestmen]], [[Solifugae|camel spiders]], [[Amblypygi|whip spiders]] and [[Uropygi|vinegaroons]].<ref>{{cite book |editor1-first=Joel |editor1-last=Cracraft |editor2-first=Michael |editor2-last=Donoghue |title=Assembling the Tree of Life|url=https://archive.org/details/assemblingtreeli00crac_335 |url-access=limited |publisher=[[Oxford University Press]] |date=2004 |page=[https://archive.org/details/assemblingtreeli00crac_335/page/n314 297] |name-list-style=amp}}</ref>

Adult arachnids have eight [[Arthropod leg|legs]] attached to the  [[cephalothorax]]. In some species the frontmost pair of legs has converted to a sensory function, while in others, different [[appendage]]s can grow large enough to take on the appearance of extra pairs of legs.

Almost all [[Extant taxon|extant]] arachnids are [[terrestrial animal|terrestrial]], living mainly on land. However, some inhabit freshwater environments and, with the exception of the [[pelagic zone]], marine environments as well. They comprise over 110,000 named [[species]], of which 51,000 are species of spiders.<ref>{{Cite book|last=Brabazon|first=Anthony|title=Foraging-Inspired Optimisation Algorithms|publisher=Springer International Publishing|year=2018|isbn=9783319591568|pages=237}}</ref><ref name=":0">{{Cite journal |last=Agnarsson |first=Ingi |date=2023 |title=Grand challenges in research on arachnid diversity, conservation, and biogeography |journal=Frontiers in Arachnid Science |volume=2 |doi=10.3389/frchs.2023.1101141 |doi-access=free }}</ref>

The term is derived from the [[Ancient Greek|Greek]] word {{lang|grc|[[wikt:ἀράχνη#Ancient Greek|ἀράχνη]]}} (''aráchnē'', 'spider'), from the myth of the hubristic human weaver [[Arachne]], who was turned into a spider.<ref>{{cite encyclopedia |title=Arachnid |encyclopedia=[[Oxford English Dictionary]] |date=1989 |edition=2nd}}</ref>