View source for Seta

{{Short description|Hair-like structure on living organisms}}
{{Other uses|Seta (disambiguation)}}
{{redirect|Setae|the town of ancient Lydia|Setae (Lydia)}}
{{wiktionary|seta}}

In [[biology]], '''setae''' ({{IPAc-en|ˈ|s|iː|t|iː}}; {{singular}} '''seta''' {{IPAc-en|ˈ|s|iː|t|ə}}; {{etymology|la|{{wikt-lang|la|saeta}}|[[bristle]]}}) are any of a number of different bristle- or [[hair]]-like structures on living [[organism]]s.

==Animal setae==

===Protostomes===
[[File:Isonychia Foreleg.jpg|thumb|Setae on the foreleg of a [[mayfly]]]]
Depending partly on their form and function, protostome setae may be called '''macrotrichia''', '''[[chaeta]]e''', '''[[Scale (insect anatomy)|scales]]''', or [[Common name|informally]], hairs. The setal membrane is not [[Cuticle|cuticularized]], so movement is possible.

[[Annelid]] setae are stiff bristles present on the body. They allow [[earthworm]]s and their relatives to attach to the surface and prevent backsliding during [[peristaltic]] motion. These hairs make it difficult to pull a worm straight from the ground. Setae in [[oligochaetes]] (the group including earthworms) are largely composed of [[chitin]].<ref>{{cite journal | last1 = Hyman | first1 = H.L. | year = 1966 | title = Further Notes on the Occurrence of Chitin in Invertebrates | url = http://www.biolbull.org/cgi/reprint/130/1/94.pdf | journal = Biological Bulletin | volume = 130 | issue = 1| pages = 1–149 | doi = 10.2307/1539955 | jstor = 1539955 }}</ref>  They are classified according to the limb to which they are attached; for instance, notosetae are attached to [[notopodia]]; neurosetae to [[neuropodia]].<ref>{{Cite journal| last1 = Butterfield | first1 = N. J.| title = A reassessment of the enigmatic Burgess Shale fossil ''Wiwaxia corrugata'' (Matthew) and its relationship to the polychaete ''Canadia spinosa'' Walcott| jstor = 2400789| journal = Paleobiology| volume = 16| issue = 3| pages = 287–303| year = 1990| doi=10.1017/s0094837300010009| bibcode = 1990Pbio...16..287B| s2cid = 88100863}}</ref> The setae on [[polychaete worm]]s are referred to as chaeta due to their differing morphology.

[[Crustacean]]s have mechano- and [[chemosensory]] setae.<ref name="isopods.nhm.org">{{cite journal | last1 = Garm | first1 = A | year = 2004 | title = Revising the definition of the crustacean seta and setal classification systems based on examinations of the mouthpart setae of seven species of decapods | url = http://isopods.nhm.org/pdfs/12763/12763.pdf | journal = Zoological Journal of the Linnean Society | volume = 142 | issue = 2| pages = 233–252 | doi=10.1111/j.1096-3642.2004.00132.x| doi-access = free }}</ref> Setae are especially present on the mouthparts of crustaceans<ref name="isopods.nhm.org"/> and can also be found on grooming limbs.<ref name="sciencedirect.com">{{cite journal | last1 = Keiler | first1 = J. | last2 = Richter | first2 = S. | year = 2011 | title = Morphological diversity of setae on the grooming legs in Anomala (Decapoda: Reptantia) revealed by scanning electron microscopy | journal = Zoologischer Anzeiger | volume = 250 | issue = 4| pages = 343–366 | doi=10.1016/j.jcz.2011.04.004| bibcode = 2011ZooAn.250..343K }}</ref> In some cases, setae are modified into scale like structures.<ref name="sciencedirect.com"/> Setae on the legs of [[krill]] and other small crustaceans help them to gather [[phytoplankton]]. It captures them and allows them to be eaten.

Setae on the [[integument]] of insects are unicellular, meaning that each is formed from a single epidermal cell of a type called a trichogen, literally meaning "bristle generator".  They are at first hollow and in most forms remain hollow after they have hardened.  They grow through and project through a secondary or accessory cell of a type called a tormogen, which generates the special flexible membrane that connects the base of the seta to the surrounding [[integument]]. Some insects, such as ''[[Eriogaster lanestris]]'' larvae, use setae as a defense mechanism, as they can cause dermatitis when they come into contact with skin.<ref>{{Cite journal|title=Caterpillar Dermatitis | pmc=1841743 | pmid=6023131|volume=2|issue = 5548|year=1967|journal=Br Med J|pages=346–8 | last1 = Hellier | first1 = FF | last2 = Warin | first2 = RP | doi=10.1136/bmj.2.5548.346}}</ref> [[Fly|Diptera]] setae are [[Bristle sensilla|bristles]] present throughout the body and function as [[Mechanoreceptor|mechanoreceptors]].

===Deuterostomes===
====Vertebrates====
[[File:Gecko foot on glass.JPG|thumb|right|Close-up of the underside of a gecko's foot as it walks on vertical glass]]
[[File:Hemidactylus_frenatus_mating,_ventral_view.jpg|thumb|[[Common house gecko]]s mating on a vertical glass window and showing [[Lamella_(surface_anatomy)|lamellae]] under the feet]]

The pads on a [[gecko]]'s feet are small hair-like [[process (anatomy)|process]]es that play a role in the animal's ability to cling to vertical surfaces.  The micrometer-scale setae branch into nanometer-scale projections called [[Spatulae (biology)|spatulae]].<ref name=Santos2007>{{cite journal |last=Santos |first=Daniel |author2=Matthew Spenko |author3=Aaron Parness |author4=Kim Sangbae |author5=Mark Cutkosky|title=Directional adhesion for climbing: theoretical and practical considerations  |journal=Journal of Adhesion Science and Technology  |year=2007 |volume=21 |issue=12–13 |pages=1317–1341|issn=0169-4243|doi=10.1163/156856107782328399 |s2cid=53470787 |quote=''Gecko "feet and toes are a hierarchical system of complex structures consisting of lamellae, setae, and spatulae. The distinguishing characteristics of the gecko adhesion system have been described [as] (1) anisotropic attachment, (2) high pulloff force to preload ratio, (3) low detachment force, (4) material independence, (5) self-cleaning, (6) anti-self sticking and (7) non-sticky default state. ... The gecko’s adhesive structures are made from ß-keratin (modulus of elasticity [approx.] 2 GPa). Such a stiff material is not inherently sticky; however, because of the gecko adhesive’s hierarchical nature and extremely small distal features (spatulae are [approx.] 200 nm in size), the gecko’s foot is able to intimately conform to the surface and generate significant attraction using van der Waals forces.''}}</ref> A [[Tokay gecko]]'s two front feet can sustain 20.1 N of force parallel to the surface using approximately 14,400 setae per mm<sup>2</sup>. This equates to ~ 6.2 pN per seta, but does not sufficiently account for the overall stickiness behavior shown by the foot pads.<ref>{{cite book|last1=Autumn|first1=K.|last2=Puthoff|first2=J.|editor=Smith, A.M., Callow, J.A.|year=2006|chapter=Properties, principles, and parameters of the gecko adhesive system|title=Biological adhesives|pages=245–280|publisher=Springer|isbn=978-3-540-31048-8}}</ref>

=== Classification uncertain ===
In 2017, a description of a new species of basal [[deuterostome]] called ''[[Saccorhytus]]'' was published. This animal appears to have seta in the pores along the side of its body.<ref name="HanMorris2017">{{cite journal |last1=Han |first1=Jian |last2=Morris |first2=Simon Conway |last3=Ou |first3=Qiang |last4=Shu |first4=Degan |last5=Huang |first5=Hai |year=2017 |title=Meiofaunal deuterostomes from the basal Cambrian of Shaanxi (China) |journal=Nature |volume=542 |issue=7640 |pages=228–231 |bibcode=2017Natur.542..228H |doi=10.1038/nature21072 |issn=0028-0836 |pmid=28135722 |s2cid=353780}}</ref> However, in 2022, ''Saccorhytus'' is considered to be an early [[Ecdysozoa|ecdysozoan]], and was described as having "lacked setae".<ref>{{Cite journal |last1=Liu |first1=Yunhuan |last2=Carlisle |first2=Emily |last3=Zhang |first3=Huaqiao |last4=Yang |first4=Ben |last5=Steiner |first5=Michael |last6=Shao |first6=Tiequan |last7=Duan |first7=Baichuan |last8=Marone |first8=Federica |last9=Xiao |first9=Shuhai |last10=Donoghue |first10=Philip C. J. |date=2022-08-17 |title=Saccorhytus is an early ecdysozoan and not the earliest deuterostome |url=https://www.nature.com/articles/s41586-022-05107-z |journal=Nature |volume=609 |issue=7927 |language=en |pages=541–546 |doi=10.1038/s41586-022-05107-z |pmid=35978194 |bibcode=2022Natur.609..541L |s2cid=251646316 |issn=1476-4687|hdl=1983/454e7bec-4cd4-4121-933e-abeab69e96c1 |hdl-access=free }}</ref>

==Fungal setae==
[[File:Phellinus gilvus setae 2.jpg|thumb|Pointed setae protruding into the fertile surface tubes of the bracket fungus ''[[Fuscoporia gilva]]'']]
In [[mycology]], "setae" refer to dark-brown, thick-walled, thornlike [[cystidia]] found in [[corticioid fungi|corticioid]] and [[polypores|poroid fungi]] in the [[family (biology)|family]] [[Hymenochaetaceae]].<ref>{{cite book |vauthors=Kirk PM, Cannon PF, Minter DW, Stalpers JA |title=Dictionary of the Fungi |url=https://archive.org/details/dictionaryfungit00kirk |url-access=limited |edition=10th |publisher=CABI |location=Wallingford |year=2008|page=[https://archive.org/details/dictionaryfungit00kirk/page/n126 116]|isbn=978-0-85199-826-8}}</ref> Though mainly microscopic, the setae of some species may be sufficiently prominent to be visible with a hand lens.

==Plant setae==
In [[botany]], "seta" refers to the stalk supporting the [[sporangium|capsule]] of a [[moss]] or [[Marchantiophyta|liverwort]] (both closely related in a clade called "Setaphyta"), and supplying it with nutrients. The seta is part of the [[sporophyte]] and has a short foot embedded in the [[gametophyte]] on which it is [[parasitic]]. Setae are not present in all mosses, but in some [[species]] they may reach 15 to 20 centimeters in height.<ref>{{aut|[[Peter H. Raven|Raven, Peter H.]]; Evert, R.F. & Eichhorn, S.E.}} (2005): ''[[Biology of Plants]]'' (7th ed.). W.H. Freeman and Company.</ref>

==Chaetoceros setae==
In the diatom family [[Chaetocerotaceae]], "seta" refers to the hairlike outgrowths of the valve, i.e. of the face of the cells.<ref name=Tomas97>Tomas, C. R., Hasle G. R., Syvertsen, E. E., Steidinger, K. A., Tangen, K., Throndsen, J., Heimdal, B. R., (1997).  ''Identifying Marine Phytoplankton'', Academic Press.</ref> These setae have a different structure than the valve. Such setae may prevent rapid sinking and also protect the cells from grazing.

==Synthetic setae==
[[Synthetic setae]] are a class of synthetic [[adhesive]]s that detach at will, sometimes called resettable adhesives, yet display substantial stickiness.  The development of such synthetic materials is a matter of current research.<ref name=Santos2007/><ref>{{cite web|url=http://www.physorg.com/news120845139.html|title=Engineers create new adhesive that mimics gecko toe hairs|website=physorg.com|access-date=19 November 2018}}</ref><ref>[http://www.physorg.com/search/search.php?search=+Gecko%2Bsetae Setae Research] {{webarchive|url=https://web.archive.org/web/20110606060332/http://www.physorg.com/search/search.php?search=+Gecko+setae |date=2011-06-06 }}</ref>

==See also==
* [[Chaeta]]
* [[Synthetic setae]]
* [[Van der Waals force#Use by geckos and arthropods|Van der Waals force]]

==References==
{{reflist|28em}}

[[Category:Plant anatomy]]
[[Category:Animal hair]]
[[Category:Fungal morphology and anatomy]]