What is Nematode?
{{Taxobox | name = Nematodes | image = Eophasma jurasicum.JPG | image_width = 250px | image_caption = ''Eophasma jurasicum'', a fossilized nematode | regnum = [[Animal]]ia | subregnum = [[Eumetazoa]] | unranked_phylum = [[Bilateria]] | phylum = '''Nematoda''' | phylum_authority = [[Karl Rudolphi|Rudolphi]], 1808 }} [[File:Caenorhabditis elegans hermaphrodite adult-en.svg|thumb|right|250px|Diagram of nematode]] The '''nematodes''' or roundworms are one of the most diverse of all [[List of animal phyla|animal phyla]]. They are one of the [[protostome]] [[phyla]]. Nematode [[species]] look very similar to one another. Over 80,000 have been described, of which over 15,000 are [[parasite|parasitic]]. It has been estimated that the total number of described and undescribed roundworms might be more than 500,000. The body structure is fairly constant. A thick cuticle gives protection, and acts as a kind of hydrostatic skeleton. ''[[Caenorhabditis elegans]]'' has had its genetics studied intensively, and it had its genome analysed in the year 1998.<ref>{{Cite web |url=http://www.apsnet.org/education/feature/celegans/ |title=APSnet Feature - Implications of sequencing the nematode Caenorhabditis elegans genome for plant nematology |access-date=2010-01-04 |archive-date=2010-06-12 |archive-url=https://web.archive.org/web/20100612232049/http://apsnet.org/education/feature/Celegans/ |url-status=dead }}</ref> DNA sequence analysis of nematodes is quite advanced, including trees of species relationship.<ref>[http://www.bionity.com/news/e/108546/]{{Dead link|date=March 2021|bot=InternetArchiveBot|fix-attempted=yes}}</ref> Cell numbers in the organs are constant within a species. Nematodes have a fixed, genetically determined number of cells, a phenomenon known as [[eutely]]. The male ''C. elegans'' has 1031 cells, a number which does not change after cell division stops at the end of the larval period. Growth is solely due to an increase in the size of individual cells.<ref>{{cite book |title=Invertebrate Zoology, 7th editio