Editing Arachnid (section)

==Locomotion==
{{See also|Arachnid locomotion}}
Most arachnids lack [[extension (kinesiology)|extensor]] muscles in the [[Anatomical terms of location#Proximal and distal|distal]] joints of their appendages. Spiders and whip scorpions extend their limbs hydraulically using the pressure of their [[hemolymph]].<ref name=Sensenig2003>{{Cite journal |doi=10.1242/jeb.00182 |pmid=12517993 |issn=1477-9145 |volume=206 |issue=4 |pages=771–784 |last1=Sensenig |first1=Andrew T. |first2=Jeffrey W. |last2=Shultz |title=Mechanics of Cuticular Elastic Energy Storage in Leg Joints Lacking Extensor Muscles in Arachnids |journal=[[Journal of Experimental Biology]] |date=February 15, 2003 |s2cid=40503319 |name-list-style=amp|doi-access= |bibcode=2003JExpB.206..771S }}</ref> [[Solifuge]]s and some [[harvestmen]] extend their knees by the use of highly elastic thickenings in the joint cuticle.<ref name=Sensenig2003/> Scorpions, pseudoscorpions and some harvestmen have evolved muscles that extend two leg joints (the femur-patella and patella-tibia joints) at once.<ref name=Shultz2005>{{Cite journal |doi=10.1002/jmor.1052100103 |pmid=29865543 |issn=1097-4687 |volume=210 |issue=1 |pages=13–31 |last=Shultz |first=Jeffrey W. |title=Evolution of locomotion in arachnida: The hydraulic pressure pump of the giant whipscorpion, ''Mastigoproctus giganteus'' (Uropygi) |journal=[[Journal of Morphology]] |date=February 6, 2005 |s2cid=46935000 }}</ref><ref name=Shultz1992>{{Cite journal |issn=1477-9145 |volume=162 |issue=1 |pages=313–329 |last=Shultz |first=Jeffrey W. |title=Muscle Firing Patterns in Two Arachnids Using Different Methods of Propulsive Leg Extension |journal=Journal of Experimental Biology |access-date=2012-05-19 |date=January 1, 1992 |doi=10.1242/jeb.162.1.313 |url=http://jeb.biologists.org/content/162/1/313|doi-access=free |bibcode=1992JExpB.162..313S }}</ref> The equivalent joints of the pedipalps of scorpions though, are extended by elastic recoil.<ref name=Sensenig2004>{{Cite journal |doi=10.1636/S02-73 |issn=0161-8202 |volume=32 |issue=1 |pages=1–10 |last1=Sensenig |first1=Andrew T. |first2=Jeffrey W. |last2=Shultz |title=Elastic energy storage in the pedipedal joints of scorpions and sun-spiders (Arachnida, Scorpiones, Solifugae) |journal=[[Journal of Arachnology]] |date=2004 |s2cid=56461501 |name-list-style=amp|url=https://www.biodiversitylibrary.org/part/228777 }}</ref>
[[File:Haeckel Arachnida.jpg|thumb|"Arachnida" from [[Ernst Haeckel]]'s [[Kunstformen der Natur]], 1904]]