Editing Seta (section)

===Protostomes===
[[File:Isonychia Foreleg.jpg|thumb|Setae on the foreleg of a [[mayfly]]]]

[[Annelid]] setae are stiff bristles present on the body. They help, for example, [[earthworm]]s 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]] (a 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>

[[Fly|Diptera]] setae are [[Bristle sensilla|bristles]] present throughout the body and function as [[Mechanoreceptor|mechanoreceptors]].

[[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]]. Depending partly on their form and function, setae may be called hairs, '''macrotrichia''', '''[[chaeta]]e''', or '''[[Scale (insect anatomy)|scales]]'''. The setal membrane is not cuticularized and movement is possible. 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>