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Animal EvolutionInterrelationships of the Living Phyla$
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Claus Nielsen

Print publication date: 2011

Print ISBN-13: 9780199606023

Published to Oxford Scholarship Online: December 2013

DOI: 10.1093/acprof:oso/9780199606023.001.0001

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Phylum Nematoda

Phylum Nematoda

(p.276) 49 Phylum Nematoda
Animal Evolution

Claus Nielsen

Oxford University Press

The Nematoda is a highly successful phylum with about 30,000 known species, but living species are believed to be in millions. All nematodes possess a remarkably similar body plan despite living in almost all kinds of habitats, both aquatic and terrestrial. The tiny free-living, terrestrial nematode Caenorhabditis elegans is a well-documented organism. Most studies have established the Nematoda as the sister group (or a further outgroup) of Nematomorpha. The phylum is divided into Adenophorea and Secernentia, but studies of small-subunit ribosomal DNA sequences show three major clades: Enoplia, Dorylaimia, and Chromadoria (which includes the Secernentia). The embryology of Tobrilus, with a coeloblastula and an embolic gastrulation, is considered representative of the ancestral type of the nematodes. Molecular phylogeny invariably places the nematodes in the Ecdysozoa, in some cases more specifically within the Cycloneuralia.

Keywords:   nematodes, Nematoda, Caenorhabditis elegans, Nematomorpha, Adenophorea, Secernentia, Enoplia, Dorylaimia, Chromadoria, embryology

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