Editing Nematomorpha (section)

==Taxonomy==
{{See also|List of bilaterial animal orders}}
Nematomorphs can be confused with nematodes, particularly [[Mermithidae|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 paler brown colour.<ref>{{Cite web |first1=Malcolm S. |last1=Bryant |first2=Robert D. |last2=Adlard |first3=Lester R.G. |last3=Cannon |year=2006 |title=Gordian Worms: Factsheet |website=[[Queensland Museum]] |url=http://www.qm.qld.gov.au/inquiry/factsheets/Gordian_Worms_20070605.pdf |access-date=2008-03-10 |url-status=dead |archive-url=https://web.archive.org/web/20080722175823/http://www.qm.qld.gov.au/inquiry/factsheets/Gordian_Worms_20070605.pdf |archive-date=2008-07-22 }}</ref>

The phylum is placed along with the [[Ecdysozoa]] clade of moulting organisms that include the [[Arthropod]]a. Their closest relatives are the nematodes. The two phyla make up the group [[Nematoida]] in the clade [[Cycloneuralia]]. During the larval stage, the animals show a resemblance to adult [[kinorhyncha]] and some species of [[Loricifera]] and [[Priapulida]], all members of the group [[Scalidophora]].<ref>[http://www.bumblebee.org/invertebrates/NEMATOMORPHA.htm Nematomorpha – Bumblebees]</ref> The earliest Nematomorph could be ''[[Maotianshania]]'', from the Lower Cambrian; this organism is, however, very different from extant species;<ref>{{Cite journal|last1= Sun|first1= W.|last2= Hou|first2= X.|year= 1987|title= Early Cambrian worms from Chengjiang, Yunnan, China: ''Maotianshania'' gen. nov.|journal= Acta Palaeontologica Sinica|volume=26|issue=3|pages=299–305|url= http://en.cnki.com.cn/Article_en/CJFDTOTAL-GSWX198703007.htm|format=Paywall}}</ref> fossilized worms resembling the modern forms have been reported from mid [[Cretaceous]] [[Burmese amber]] dated to 100 million years ago.<ref>{{Cite journal |author1=Poinar George |author2=Ron Buckley | date = September 2006 | title = Nematode (Nematoda: Mermithidae) and hairworm (Nematomorpha: Chordodidae) parasites in Early Cretaceous amber | journal = [[Journal of Invertebrate Pathology]] | volume = 93 | issue = 1| pages = 36–41 | doi = 10.1016/j.jip.2006.04.006 | pmid = 16737709 |bibcode=2006JInvP..93...36P }}</ref>

Relationships within the phylum are still somewhat unclear, but two classes are recognised. The five marine species of nematomorph are contained in [[Nectonematoida]].<ref name="PechenikTaxo">Pechenik, '''Biology of the Invertebrates'', 2010, pg 457.</ref> This order is monotypic containing the genus ''[[Nectonema]]'' <small>Verrill, 1879</small>: adults are planktonic and the larvae parasitise [[Decapoda|decapod crustaceans]], especially crabs.<ref name="PechenikTaxo"/> They are characterized by a double row of natotory [[seta]]e along each side of the body, dorsal and ventral longitudinal epidermal cords, a spacious and fluid-filled [[blastocoelom]] and singular [[gonad]]s.

The approximately 320 remaining species are distributed between two families,<ref name="itisGodioidea">{{ITIS|id=699878 |taxon=Gordioidea}}</ref> within the monotypic class [[Gordioida]]. Gordioidean adults are free-living in freshwater or semiterrestrial habitats and larvae parasitise insects, primarily [[orthoptera]]ns.<ref name="PechenikTaxo"/> Unlike nectonematiodeans, gordioideans lack lateral rows of setae, have a single, ventral epidermal cord and their blastocoels are filled with [[mesenchyme]] in young animals but become spacious in older individuals.