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 organisms.

==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''', '''chaetae''', '''scales''', or informally, hairs. The setal membrane is not cuticularized, so movement is possible.<ref>{{Cite book |last=Torre-Bueno |first=J. R. de la (José Rollin) |url=http://archive.org/details/torrebuenoglossa0000torr |title=The Torre-Bueno glossary of entomology |date=1989 |publisher=New York, N.Y., USA : New York Entomological Society in cooperation with the American Museum of Natural History |others=Internet Archive |isbn=978-0-913424-13-1}}</ref> ====Annelid==== Annelid setae are stiff bristles present on the body. They allow earthworms 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 worms are referred to as chaeta due to their differing morphology.<ref>{{Cite book |last=Fauchald |first=Kristian |date=1977 |title=The polychaete worms. Definitions and keys to the orders, families and genera |url=http://hdl.handle.net/10088/3435 |language=en-US|publisher=Natural History Museum of Los Angeles County|location=Los Angeles, California}}</ref>

====Crustacean==== Crustaceans 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.<ref>{{Cite journal |last=Hamner |first=W. M. |date=1988-04-01 |title=Biomechanics of Filter Feeding in the Antarctic Krill Euphausia Superba: Review of Past Work and New Observations |url=https://academic.oup.com/jcb/article-lookup/doi/10.2307/1548308 |journal=Journal of Crustacean Biology |language=en |volume=8 |issue=2 |pages=149–163 |doi=10.2307/1548308 |issn=0278-0372|url-access=subscription }}</ref>

====Insect==== 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> Diptera setae are bristles present throughout the body and function as mechanoreceptors.

===Deuterostomes=== ====Vertebrates==== 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 geckos mating on a vertical glass window and showing lamellae under the feet]]

The pads on a gecko's feet are small hair-like processes 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.<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 mm². 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 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 and poroid fungi in the 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 capsule of a moss or 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|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.<ref>{{Cite journal |last=Owari |first=Yuka |last2=Nakamura |first2=Fumi |last3=Oaki |first3=Yuya |last4=Tsuda |first4=Hiroyuki |last5=Shimode |first5=Shinji |last6=Imai |first6=Hiroaki |date=2022-05-09 |title=Ultrastructure of setae of a planktonic diatom, Chaetoceros coarctatus |url=https://www.nature.com/articles/s41598-022-11484-2 |journal=Scientific Reports |language=en |volume=12 |issue=1 |pages=7568 |doi=10.1038/s41598-022-11484-2 |issn=2045-2322|pmc=9085750 }}</ref>

==Synthetic setae== Synthetic setae are a class of synthetic adhesives 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

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

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