Editing Scorpion (section)

===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 -->