Nematomorpha
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2008-07-14T19:54:12Z
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{{Taxobox | name = Nematomorpha
| image = Paragordius tricuspidatus.jpeg
| image_width = 250px
| caption = ''[[Paragordius tricuspidatus]]''
| domain = ''[[Eukaryota]]''
| regnum = [[Animal]]ia
| phylum = '''Nematomorpha'''
| phylum_authority = [[Vejdovsky]], 1886
| subdivision_ranks = [[Class (biology)|Classes]]
| subdivision = [[Nectonematoida]]<br/>[[Gordioidea]]
}}
'''Nematomorpha''' (sometimes called '''Gordiacea''', and commonly known as '''Horsehair worms''' or '''Gordian worms''') are a [[phylum]] of [[parasitic]] [[animal]]s which are [[morphology (biology)|morphologically]] and [[ecology|ecologically]] similar to [[nematode]] worms, hence the name. They are, on average, 1 [[meter]] long, and 1 to 3 [[millimetre]]s in diameter. Horsehair worms can be discovered in damp areas such as watering troughs, streams, puddles, and cisterns. The adult worms are free living, but the [[larva]]e are [[parasite|parasitic]] on [[beetle]]s, [[cockroach]]es, [[grasshopper]]s and [[crustacean]]s. About 320 species have been described.
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. Reproductively, they are [[dioecious]], with the internal fertilization of eggs that are then laid in gelatinous strings.
Nematomorphs can be confused with nematodes, particularly Mermithid worms. Unlike Nematomorphs, Mermithids do not have a terminal cloaca. Male mermithids have one or two spicules just before the end apart from having a thinner, smoother cuticle, without areoles and a paler brown colour.<ref>Malcolm S. Bryant, Robert D. Adlard & Lester R.G. Cannon 2006. Gordian Worms: Factsheet. Queensland Museum. [http://www.qm.qld.gov.au/inquiry/factsheets/Gordian_Worms_20070605.pdf]</ref>
[[Image:Spinochordodes in Meconema.jpg|thumb|250px|left|''[[Spinochordodes tellinii]]'' and its katydid host]]
In ''[[Spinochordodes tellinii]]'', which has grasshoppers as its [[vector (biology)|vector]], the infection acts on the grasshopper's brain and causes it to seek water and drown itself, thus returning the nematomorph to water.<ref>{{cite journal |quotes=no | last = Thomas | first = F. | coauthors = Schmidt-Rhaesa, A., Martin, G., Manu, C., Durand, P., and Renaud, F. | year = 2002 | month = May | title = Do hairworms (Nematomorpha) manipulate the water seeking behaviour of their terrestrial hosts? | journal = [[Journal of evolutionary biology|J. Evol. Biol.]] | volume = 15 | issue = 3 | pages = 356–361 | id = {{ISSN|1010-061X}} |url=http://www.erin.utoronto.ca/~w3gwynne/BIO418/Nemato.pdf | doi = 10.1046/j.1420-9101.2002.00410.x}} — 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> They are also remarkably able to survive the predation of their host, being able to wriggle out of the predator which has eaten the host cricket.<ref>{{cite journal |quotes=no | last = Ponton | first = Fleur | coauthors = Camille Lebarbenchon, Thierry Lefèvre, David G. Biron, David Duneau, David P. Hughes, and Frédéric Thomas | year = 2006 | month = April | title = Parasitology: Parasite survives predation on its host | journal = [[Nature (journal)|Nature]] | volume = 440 | issue = 7085 | page = 756 | doi = 10.1038/440756a | pages = 756}}</ref>
Relationships within the phylum are still somewhat unclear, but two classes are recognised:
*Class [[Nectonematoida]]: Marine, planktonic, with a double row of natotory [[seta]]e along each side of the body; with dorsal and ventral longitudinal epidermal cords, [[blastocoelom]] spacious and fluid filled; [[gonad]]s single; larvae parasitise [[Decapoda|decapod crustaceans]]
*Class [[Gordioidea]]: Freshwater and semiterrestrial; lack lateral rows of setae; with a single, ventral epidermal cord; blastocoelom filled with [[mesenchyme]] in young animals but becomes spacious in older individuals; larvae parasitise grasshoppers and [[cricket]]s
==References==
{{reflist}}
==External links==
*[http://www.canal.ird.fr/canal.php?url=/programmes/recherches/grillons_us/index.htm The cricket suicide (video)]
* [http://www.nature.com/nature/journal/v440/n7085/suppinfo/440756a.html Videos of a cricket infected with a Gordian worm] with the worm emerging to mate, as well as emerging from predators which have eaten the infected cricket. From ''[[Nature (journal)|Nature]]'', April 2006.
* [http://www.youtube.com/watch?v=xu9bqt2OgFM YouTube video of worms crawling out of a crushed grasshopper.]
[[Category:parasitic animals]][[Category:Psuedocoelomates]]
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