Nematoda

English: Nematodes; Nemetoudz; Roundworms.
Members: 80000 species described, 15000 are parasitic; estimated more than 500,000.
Habitat:adapted to nearly every ecological niche; marine to fresh water to terrestrial environments; polar regions, Antarctica to the tropics; highest to the lowest of elevations.ZoologyTypical: Nematodes are very difficult to distinguish; represent 90% of all life on the seafloor.
Worms; mostly parasitic, on plants, animals, humans; some nematodes can undergo cryptobiosis.
Body: tubular digestive systems with openings at both ends.TaxonomyThere is lack of knowledge regarding many nematodes. Traditionally, they are divided into two classes, the Adenophorea and the Secernentea. DNA studies suggested the existence of five clades: Dorylaimia, Enoplia, Spirurina, Tylenchina, Rhabditina.
Secernentea are indeed a natural group of closest relatives. Adenophorea appear to be a paraphyletic assemblage of roundworms simply retaining a good number of ancestral traits. The Enoplia do not seem to be monophyletic either but to contain two distinct lineages. The old group Chromadoria seem to be paraphyletic, with the Monhysterida representing a very ancient minor group of nematodes. Among the Secernentea, the Diplogasteria may need to be united with the Rhabditia. while the Tylenchia might be paraphyletic with the Rhabditia.The understanding of roundworm systematics and phylogeny as of 2002 is summarised below:
Phylum Nematoda
Basal order Monhysterida
Basal subclass/Class Enoplia
Basal subclass/Class Dorylaimia
Class Secernentea
Subclass Diplogasteria (disputed)
Subclass Rhabditia (paraphyletic?)
Subclass Spiruria
Subclass Tylenchia (disputed)
"Chromadoria" assemblage