Editing Nematomorpha (section)

==Description and biology==
Nematomorphs possess an external [[cuticle]] without [[cilia]]. Internally, they have only longitudinal muscle and a non-functional gut, with no [[excretory system|excretory]], [[respiratory system|respiratory]] or [[circulatory system]]s. The nervous system consists of a [[nerve ring]] near the anterior end of the animal and a [[ventral nerve cord]] running along the body.<ref name=IZ>{{Cite book |author= Barnes, Robert D. |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location= Philadelphia, PA|pages= 307–308|isbn= 978-0-03-056747-6}}</ref>

Reproductively, they have [[Dioecy|two distinct sexes]], with the internal fertilization of eggs that are then laid in gelatinous strings. Adults have cylindrical [[gonad]]s, opening into the [[cloaca]]. The larvae have rings of cuticular hooks and terminal stylets that are believed to be used to enter the hosts. Once inside the host, the larvae live inside the [[haemocoel]] and absorb nutrients directly through their skin. Development into the adult form takes weeks or months, and the larva [[ecdysis|moults]] several times as it grows in size.<ref name=IZ/>

The adults are mostly free-living in freshwater or marine environments, and males and females aggregate into tight balls (''Gordian knots'') during mating.<ref name=manipulate/><ref>{{Cite journal|first=Andreas|last=Schmidt-Rhaesa|year=2002|title=Two Dimensions of Biodiversity Research Exemplified by Nematomorpha and Gastrotricha|journal=Integrative and Comparative Biology|volume=42|issue=3|pages=633–640|doi=10.1093/icb/42.3.633|pmid=21708759 |doi-access=free}}</ref>

[[Image:Spinochordodes in Meconema.jpg|thumb|left|''[[Spinochordodes tellinii]]'' and its ''[[Meconema]]'' host]]
In ''[[Spinochordodes tellinii]]'' and ''[[Paragordius tricuspidatus]]'', which have [[grasshoppers]] and [[crickets]] as their hosts, the infection acts on the infected host's brain.<ref>{{cite journal |doi = 10.1016/S0020-7519(03)00014-6 |author = Thomas, F.|year=2003 |title=Biochemical and histological changes in the brain of the cricket ''Nemobius sylvestris'' infected by a manipulative parasite ''Paragordius tricuspudatus'' (Nematomorpha) |journal=[[International Journal for Parasitology]] |volume=33 |pages=435–443 |issue = 4| pmid=12705936 | url=https://hal.science/hal-00307180 |display-authors=etal}}</ref> This causes the host insect to seek water and drown itself, thus returning the nematomorph to water.<ref name=manipulate>{{Cite journal |last = Thomas |first = F. |author2 = Schmidt-Rhaesa, A. |author3 = Martin, G. |author4 = Manu, C. |author5 = Durand, P. |author6 = Renaud, F. |date = May 2002 |title = Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts? |journal = [[Journal of Evolutionary Biology]] |volume = 15 |issue = 3 |pages = 356–361 |url = http://www.erin.utoronto.ca/~w3gwynne/BIO418/Nemato.pdf |doi = 10.1046/j.1420-9101.2002.00410.x |url-status = dead |archive-url = https://web.archive.org/web/20150924002153/http://www.erin.utoronto.ca/~w3gwynne/BIO418/Nemato.pdf |archive-date = 2015-09-24 |citeseerx = 10.1.1.485.9002 |s2cid = 86278524 }} — according to Thomas ''et al.'', the "infected insects may first display an erratic behaviour which brings them sooner or later close to a stream and then a behavioural change that makes them enter the water", rather than seeking out water over long distances.</ref> ''P. tricuspidatus'' is also remarkably able to survive the predation of their host, being able to wiggle out of the predator that has eaten the host.<ref>{{Cite journal |last = Ponton |first = Fleur |author2=Camille Lebarbenchon |author3=Thierry Lefèvre |author4=David G. Biron |author5=David Duneau |author6=David P. Hughes |author7=Frédéric Thomas |date=April 2006 |title = Parasitology: Parasite survives predation on its host |journal = [[Nature (journal)|Nature]] |pmid = 16598248 |volume = 440 |issue = 7085 |doi = 10.1038/440756a |page = 756 |bibcode = 2006Natur.440..756P |s2cid = 7777607 |url = https://hal.umontpellier.fr/hal-02992927/file/Ponton%20et%20al%202006%20nature.pdf }}</ref> The nematomorpha parasite affects host ''[[Hierodula patellifera]]''{{'}}s light-interpreting organs so the host is attracted to horizontally [[Polarization (waves)|polarized light]]. Thus the host goes into water and the parasite's lifecycle completes.<ref>{{Cite web|title=Parasites manipulate praying mantis's polarized-light perception, causing it to jump into water|url=https://phys.org/news/2021-06-parasites-mantis-polarized-light-perception.html|access-date=2021-07-04|website=phys.org|language=en}}</ref> Many of the genes the parasites use for manipulating their host have been acquired through [[horizontal gene transfer]] from the host genome.<ref>[https://www.popularmechanics.com/science/animals/a45575538/horsehair-worm-horizontal-gene-transfer/ This Parasitic Worm 'Steals' Genes From Its Unsuspecting Host]</ref>

There are a few cases of accidental parasitism in vertebrate hosts, including dogs,<ref>{{Cite journal |doi=10.3347/kjp.2015.53.6.719 |pmid=26797439|title=A Horsehair Worm, ''Gordius'' sp. (Nematomorpha: Gordiida), Passed in a Canine Feces |journal=The Korean Journal of Parasitology |volume=53 |issue=6 |pages=719–24 |year=2015 |last1=Hong |first1=Eui-Ju |last2=Sim |first2=Cheolho |last3=Chae |first3=Joon-Seok |last4=Kim |first4=Hyeon-Cheol |last5=Park |first5=Jinho |last6=Choi |first6=Kyoung-Seong |last7=Yu |first7=Do-Hyeon |last8=Yoo |first8=Jae-Gyu |last9=Park |first9=Bae-Keun |pmc=4725239}}</ref> cats,<ref>{{Cite journal |last1=Saito |first1=Y |last2=Inoue |first2=I |last3=Hayashi |first3=F |last4=Itagaki |first4=H |year=1987 |title=A hairworm, Gordius sp., vomited by a domestic cat |journal=Nihon Juigaku Zasshi. The Japanese Journal of Veterinary Science |volume=49 |issue=6 |pages=1035–7 |doi=10.1292/jvms1939.49.1035 |pmid=3430914 |doi-access=free}}</ref> and humans. Several cases involving ''Parachordodes'', ''Paragordius'', or ''Gordius'' have been recorded in human hosts in Japan and China.<ref>{{Cite journal|doi=10.3347/kjp.2012.50.3.263|pmid=22949758|title=Two Human Cases Infected by the Horsehair Worm, Parachordodes sp. (Nematomorpha: Chordodidae), in Japan and America |journal=The Korean Journal of Parasitology |volume=50 |issue=3 |pages=263–7 |year=2012 |last1=Yamada |first1=Minoru |last2=Tegoshi |first2=Tatsuya |last3=Abe |first3=Niichiro |last4=Urabe |first4=Misako|pmc=3428576}}</ref>