Editing Scorpion (section)

==Morphology==

[[File:Scorpion anatomy.svg|thumb|Scorpion anatomy (dorsal view of ''[[Cheloctonus jonesii]]''):<br /> 1 = Cephalothorax or [[prosoma]];<br /> 2 = Preabdomen or [[mesosoma]];<br /> 3 = Tail or [[metasoma]];<br /> 4 = Claws or [[pedipalp]]s;<br /> 5 = Legs;<br /> 6 = Mouth parts or [[chelicerae]];<br /> 7 = Pincers or [[chelae]];<br /> 8 = Moveable claw or tarsus;<br /> 9 = Fixed claw or manus;<br /> 10 = [[Stinger]] or aculeus;<br /> 11 = [[Telson]] (anus in previous joint);<br /> 12 = Opening of book lungs]]

Scorpions range in size from the {{convert|8.5|mm|in|abbr=on|adj=on}} ''[[Typhlochactas mitchelli]]'' of Typhlochactidae,<ref name="Earthlife"/> to the {{convert|23|cm|in|abbr=on|adj=on}} ''[[Heterometrus swammerdami]]'' of Scorpionidae.<ref>{{cite book |first=Manny |last=Rubio |year=2000 |title=Scorpions: Everything About Purchase, Care, Feeding, and Housing |publisher=[[Barron's Educational Series|Barron's]] |isbn=978-0-7641-1224-9 |chapter=Commonly Available Scorpions |pages=26–27 |chapter-url=https://archive.org/details/scorpionscomplet00mann/page/26 |quote=The Guinness Book of Records claims [...] ''Heterometrus swammerdami'', to be the largest scorpion in the world [9 inches (23 cm)]}}</ref> The body of a scorpion is divided into two parts or [[Tagma (biology)|tagmata]]: the [[cephalothorax]] or [[prosoma]], and the abdomen or [[opisthosoma]].{{efn|As there is currently neither paleontological nor embryological evidence that arachnids ever had a separate thorax-like division, there exists an argument against the validity of the term cephalothorax, which means fused [[cephalon (arthropod anatomy)|cephalon]] (head) and the [[Thorax (arthropod anatomy)|thorax]]. Similarly, arguments can be formed against use of the term abdomen, as the opisthosoma of all scorpions contains a heart and book lungs, organs atypical of an abdomen.<ref>{{cite book |last1=Shultz |first1=Stanley |last2=Shultz |first2=Marguerite |title=The Tarantula Keeper's Guide |date=2009 |publisher=Barron's |isbn=978-0-7641-3885-0 |page=23}}</ref>}} The opisthosoma is subdivided into a broad anterior portion, the [[mesosoma]] or pre-abdomen, and a narrow tail-like posterior, the [[metasoma]] or post-abdomen.{{sfn|Polis|1990|pp=10–11}} External differences between the sexes are not obvious in most species. In some, the metasoma is more elongated in males than females.{{sfn|Stockmann|Ythier|2010|p=76}}

===Cephalothorax===

The cephalothorax comprises the [[carapace]], eyes, chelicerae (mouth parts), [[pedipalp]]s (which have [[chelae]], commonly called claws or pincers) and four pairs of [[walking leg]]s. Scorpions have two eyes on the top of the cephalothorax, and usually two to five pairs of eyes along the front corners of the cephalothorax. While unable to form sharp images, their central eyes are amongst the most light sensitive in the animal kingdom, especially in dim light, which makes it possible for nocturnal species to use starlight to navigate at night.<ref name="Chakravarthy Sridhara 2016">{{cite book |last1=Chakravarthy |first1=Akshay Kumar |last2=Sridhara |first2=Shakunthala |title=Arthropod Diversity and Conservation in the Tropics and Sub-tropics |url=https://books.google.com/books?id=wLiVDQAAQBAJ&pg=PA60 |year=2016 |publisher=Springer |isbn=978-981-10-1518-2 |page=60 |access-date=11 September 2017 |archive-date=31 May 2021 |archive-url=https://web.archive.org/web/20210531031224/https://books.google.com/books?id=wLiVDQAAQBAJ&pg=PA60 |url-status=live }}</ref> The chelicerae are at the front and underneath the carapace. They are pincer-like and have three segments and sharp "teeth".{{sfn|Polis|1990|pp=16–17}}{{sfn|Stockmann|2015|p=26}} The brain of a scorpion is in the back of the cephalothorax, just above the [[esophagus]].{{sfn|Polis|1990|p=38}} As in other arachnids, the nervous system is highly concentrated in the cephalothorax, but has a long ventral nerve cord with segmented [[ganglia]] which may be a [[Primitive (phylogenetics)|primitive]] trait.{{sfn|Polis|1990|p=342}}

The pedipalp is a segmented, clawed [[appendage]] used for prey immobilization, defense and sensory purposes. The segments of the pedipalp (from closest to the body outward) are coxa, trochanter, femur, patella, tibia (including the fixed claw and the manus) and tarsus (moveable claw). A scorpion has darkened or granular raised linear ridges, called "keels" or "carinae" on the pedipalp segments and on other parts of the body; these are useful as taxonomic [[phenotypic trait|characters]].{{sfn|Polis|1990|p=12}} Unlike those of some other arachnids, the legs have not been modified for other purposes, though they may occasionally be used for digging, and females may use them to catch emerging young. The legs are covered in [[proprioceptor]]s, [[bristle]]s and sensory [[setae]].{{sfn|Polis|1990|p=20}} Depending on the species, the legs may have spines and spurs.{{sfn|Polis|1990|p=74}}

===Mesosoma===

[[File:Vista ventral de un escorpión.jpg|thumb|upright|right<!--left-->|Ventral view: the [[pectines]] have a comblike structure in an inverted V shape.]]

The mesosoma or preabdomen is the broad part of the opisthosoma.{{sfn|Polis|1990|pp=10–11}} In the early stages of embryonic development the mesosoma consist of eight segments, but the first segment disappear before birth, so the mesosoma in scorpions actually consist of segments 2-8.<ref>{{Cite journal|title=The ultrastructure of book lung development in the bark scorpion Centruroides gracilis (Scorpiones: Buthidae) - PMC|year=2011 |pmc=3199777 |last1=Farley |first1=R. D. |journal=Frontiers in Zoology |volume=8 |page=18 |doi=10.1186/1742-9994-8-18 |pmid=21791110 |doi-access=free }}</ref><ref>{{Cite web|url=http://www.sharmalabuw.org/uploads/1/3/6/1/13619635/schwager_et_al._2015.pdf|title=Chelicerata - Prashant P. Sharma}}</ref><ref>{{Cite web|url=http://www.science.marshall.edu/fet/euscorpius/p2011_120.pdf|title=Euscorpius - Marshall University}}</ref> These [[anterior]] seven [[somite]]s (segments) of the opisthosoma are each covered [[Anatomical terms of location|dorsally]] by a sclerotized plate called the [[tergite]]. [[Ventral]]ly, somites 3 to 7 are armored with matching plates called [[sternites]]. The ventral side of somite 1 has a pair of genital [[Operculum (animal)|opercula]] covering the [[gonopore]]. Sternite 2 forms the basal plate bearing the [[pectines]],{{sfn|Polis|1990|pp=13–14}} which function as sensory organs.<ref name="Knowlton Gaffin 2011">{{cite journal |last1=Knowlton |first1=Elizabeth D. |last2=Gaffin |first2=Douglas D. |title=Functionally Redundant Peg Sensilla on the Scorpion Pecten |journal=Journal of Comparative Physiology A |publisher=Springer |volume=197 |issue=9 |year=2011 |issn=0340-7594 |doi=10.1007/s00359-011-0650-9 |pages=895–902|pmid=21647695 |s2cid=22123929 }}</ref>

The next four somites, 3 to 6, all bear pairs of [[Spiracle (arthropods)|spiracles]]. They serve as openings for the scorpion's respiratory organs, known as [[book lungs]]. The spiracle openings may be slits, circular, elliptical or oval according to the species.{{sfn|Polis|1990|p=15}}<ref name="Wanninger 2015">{{cite book |last=Wanninger |first=Andreas |title=Evolutionary Developmental Biology of Invertebrates 3: Ecdysozoa I: Non-Tetraconata |url=https://books.google.com/books?id=rxZcCgAAQBAJ&pg=PA105 |year=2015 |publisher=Springer |isbn=978-3-7091-1865-8 |page=105 |access-date=11 September 2017 |archive-date=5 August 2020 |archive-url=https://web.archive.org/web/20200805003251/https://books.google.com/books?id=rxZcCgAAQBAJ&pg=PA105 |url-status=live }}</ref> There are thus four pairs of book lungs; each consists of some 140 to 150 thin [[lamella (surface anatomy)|lamellae]] filled with air inside a pulmonary chamber, connected on the ventral side to an atrial chamber which opens into a spiracle. Bristles hold the lamellae apart. A muscle opens the spiracle and widens the atrial chamber; dorsoventral muscles contract to compress the pulmonary chamber, forcing air out, and relax to allow the chamber to refill.{{sfn|Polis|1990|pp=42–44}} The 7th and last somite does not bear appendages or any other significant external structures.{{sfn|Polis|1990|p=15}}

The mesosoma contains the heart or "dorsal vessel" which is the center of the scorpion's [[open circulatory system]]. The heart is continuous with a deep arterial system which spreads throughout the body. Sinuses return deoxygenated blood ([[hemolymph]]) to the heart; the blood is re-oxygenated by cardiac pores. The mesosoma also contains the reproductive system. The female [[gonad]]s are made of three or four tubes that run parallel to each other and are connected by two to four transverse [[anastomoses]]. These tubes are the sites for both [[oocyte]] formation and embryonic development. They connect to two [[oviduct]]s which connect to a single atrium leading to the genital orifice.{{sfn|Stockmann|2015|pp=45–46}} Males have two gonads made of two cylindrical tubes with a ladder-like configuration; they contain cysts which produce [[spermatozoa]]. Both tubes end in a [[spermiduct]], one on each side of the mesosoma. They connect to glandular symmetrical structures called paraxial organs, which end at the genital orifice. These secrete [[chitin]]-based structures which come together to form the [[spermatophore]].{{sfn|Stockmann|2015|p=47}}<ref>{{cite journal |last1=Lautié |first1=N. |last2=Soranzo |first2=L. |last3=Lajarille |first3=M.-E. |last4=Stockmann |first4=R. |year=2007 |title=Paraxial Organ of a Scorpion: Structural and Ultrastructural Studies of ''Euscorpius tergestinus'' Paraxial Organ (Scorpiones, Euscorpiidae) |journal=Invertebrate Reproduction & Development |volume=51 |issue=2 |pages=77–90 |doi=10.1080/07924259.2008.9652258 |s2cid=84763256 }}</ref>

===Metasoma===

[[File:ScorpionBarb.jpg|thumb|upright|left|Stinger of an [[Arizona bark scorpion]] ]]

The "tail" or metasoma consists of five segments and the [[telson]], which is not strictly a segment. The five segments are merely body rings; they lack apparent sterna or terga, and become larger distally. These segments have keels, setae and bristles which may be used for taxonomic classification. The anus is at the distal and ventral end of the last segment, and is encircled by four anal papillae and the anal arch.{{sfn|Polis|1990|p=15}} The tails of some species contain light receptors.<ref name="Chakravarthy Sridhara 2016"/>

The telson includes the [[vesicle (biology and chemistry)|vesicle]], which contains a symmetrical pair of [[venom gland]]s. Externally it bears the curved stinger, the hypodermic aculeus, equipped with sensory hairs. Each of the venom glands has its own duct to convey its secretion along the aculeus from the bulb of the gland to immediately near of the tip, where each of the paired ducts has its own venom pore.<ref name="Yigit Benli 2010">{{cite journal |last1=Yigit |first1=N. |last2=Benli |first2=M. |title=Fine Structural Analysis of the Stinger in Venom Apparatus of the Scorpion ''Euscorpius mingrelicus'' (Scorpiones: Euscorpiidae) |journal=Journal of Venomous Animals and Toxins Including Tropical Diseases |date=2010 |volume=16 |issue=1 |pages=76–86 |doi=10.1590/s1678-91992010005000003 |doi-access=free}}</ref> An extrinsic muscle system in the tail moves it forward and propels and penetrates with the aculeus, while an intrinsic muscle system attached to the glands pumps venom through the stinger into the intended victim.{{sfn|Stockmann|2015|p=30}} The stinger contains [[metalloprotein]]s with zinc, hardening the tip.<ref>{{cite book |last=Schofield |first=R. M. S. |year=2001 |chapter=Metals in cuticular structures |title=Scorpion Biology and Research |editor1=Brownell, P. H. |editor2=Polis, G. A. |pages=234–256 |location=New York |publisher=Oxford University Press |isbn=978-0195084344}}</ref> The optimal stinging angle is around 30 degrees relative to the tip.<ref>{{cite journal |last1=van der Meijden |first1=Arie |last2=Kleinteich |first2=Thomas |title=A biomechanical view on stinger diversity in scorpions |journal=Journal of Anatomy |date=April 2017 |volume=230 |issue=4 |pages=497–509 |doi=10.1111/joa.12582|pmid=28028798 |pmc=5345679 |doi-access=free }}</ref><!-- +chitin fibril https://www.researchgate.net/publication/282399934_Study_of_biomechanical_anatomical_and_physiological_properties_of_scorpion_stingers_for_developing_biomimetic_materials -->