Editing Telson

{{Short description|Hindmost division of an arthropod body}}
{{For|the copepod (genus)|Telson (copepod)}}

[[Image:Penaeus diagram telson.png|upright=1.4|thumb|right|Diagram highlighting the telson of the prawn ''[[Litopenaeus setiferus]]'']][[File:Carcinoscorpius rotundicauda.jpg|thumb|Telson (arrow no. 3) of the horseshoe crab ''[[Carcinoscorpius rotundicauda]]'']]

The '''telson''' ({{ety|grc|τέλσον|headlands, limit}}) is the hindmost division of the body of an [[arthropod]]. Depending on the definition, the telson is either considered to be the final [[segment (biology)|segment]] of the arthropod body, or an additional division that is not a true segment on account of not arising in the embryo from [[teloblast]] areas as other segments.<ref>{{Cite web|title=Crustacea Glossary::Definitions|url=https://research.nhm.org/glossary/define.html?termID=769|access-date=2021-08-03|website=research.nhm.org}}</ref> It never carries any [[appendage]]s, but a forked "tail" called the caudal furca may be present. The shape and composition of the telson differs between arthropod groups.

==Crustaceans==
In [[lobster]]s, [[Caridea|shrimp]] and other [[Decapoda|decapods]], the '''telson''', along with the [[uropod]]s, forms the '''tail fan'''. This is used as a paddle in the [[caridoid escape reaction]] ("lobstering"), whereby an alarmed animal rapidly flexes its tail, causing it to dart backwards. [[Krill]] can reach speeds of over 60&nbsp;cm per second by this means. The [[Induction period|trigger]] time to optical [[stimulus (physiology)|stimulus]] is, in spite of the low temperatures, only 55&nbsp;[[milliseconds]].

In the [[Isopoda]] and [[Tanaidacea]] (superorder [[Peracarida]]), the last abdominal body segment is fused with the telson, forming a "pleotelson".<ref>{{cite web |url=http://www.crustacea.net/crustace/isopoda/index.htm |title=Australian Isopoda: Families |author=S. J. Keable, G. C. B. Poore & G. D. F. Wilson |publisher=[[Australian Museum]] |date=October 2, 2002}}</ref>

==Chelicerates==
[[File:Scorpion_Photograph_By_Shantanu_Kuveskar.jpg|thumb|''[[Hottentotta tamulus]]'' scorpion, showing telson]]
The term ''telson'' is widely used for the [[caudal spine]] of some [[Chelicerata|chelicerates]].<ref>{{cite book |author=Richard C. Brusca & Gary J. Brusca |year=2003 |title=Invertebrates |url=https://archive.org/details/invertebratesnde00brus |url-access=limited |edition=2nd |publisher=[[Sinauer Associates]] |pages=[https://archive.org/details/invertebratesnde00brus/page/n670 1]–936 |isbn=0-87893-097-3}}</ref><ref>{{cite book |author=E. E. Ruppert & R. D. Barnes |year=1994 |title=Invertebrate Zoology |edition=6th |publisher=[[Saunders (publisher)|Saunders]] |isbn=0-03-026668-8 |url-access=registration |url=https://archive.org/details/invertebratezool0006rupp }}</ref> The chelicerate telson can be clearly seen in a number of fossil species (like in [[eurypterid]]s) and in extant animals (like the [[horseshoe crab]] "tail" and the [[scorpion]] sting). Some authorities have urged that the usage of this word in this context be discouraged.{{Why|date=August 2014}}<ref>{{cite journal |author=Karl-Ernst Lauterbach |year=1980 |title=Schlüsselereignisse in der Evolution des Grundplans der Arachnata (Arthropoda) |language=de |trans-title=Key events in the evolution of the ground plan of the Arachnata (Arthropoda) |journal=Abhandlungen des Naturwissenschaftlichen Vereins in Hamburg |series=NF |volume=23 |pages=163–327}}</ref>

==Myriapods==
[[File:Millipede telson.jpg|thumb|Telson of a millipede, including an epiproct (e), hypoproct (h) and paraprocts (p)]]
In [[millipedes]], the telson consists of a legless pre-anal body segment (which may contain a posterior extension known as an ''epiproct''), a pair of anal valves (''paraprocts'') or plates closing off the anus, and a plate below the anus (''hypoproct''), also known as a subanal scale.<ref name=SierwaldBond2007>{{cite journal|last=Sierwald|first=Petra|author2=Bond, Jason E. |title=Current Status of the Myriapod Class Diplopoda (Millipedes): Taxonomic Diversity and Phylogeny|journal=Annual Review of Entomology|year=2007|volume=52|issue=1|pages=401–420|doi=10.1146/annurev.ento.52.111805.090210|pmid=17163800}}</ref><ref>{{cite web|last=Mesibov|first=Robert|title=Tail|url=http://www.polydesmida.info/polydesmida/tail.html|work=External Anatomy of Polydesmida|access-date=4 November 2013}}</ref>

In [[centipedes]] the telson is the hindmost body segment, posterior to the genital openings, bearing two anal valves.<ref name="Lewis 2008">{{cite book|last=Lewis|first=J. G. E.|title=The Biology of Centipedes.|year=2008|publisher=[[Cambridge University Press]]|location=Cambridge|isbn=9780521034111|edition=Digitally printed 1st paperback version.}}</ref>

==Hexapods==
[[Protura]]ns, an order of minute soil-dwelling animals, are the only [[Hexapoda|hexapods]] with a telson.<ref>[https://academic.oup.com/mbe/article/22/7/1579/974202?login=false The Phylogenetic Positions of Three Basal-Hexapod Groups (Protura, Diplura, and Collembola) Based on Ribosomal RNA Gene Sequences]</ref>

==See also==
*[[Opisthosoma]]
*[[Pygidium]]

==References==
{{reflist}}

[[Category:Crustacean anatomy]]
[[Category:Arthropod anatomy]]