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Nematoda (nematode worms or roundworms)
Life
> Eukaryotes >
Opisthokonta >
Bilateria >
Ecdysozoa >
Introverta > Nematoida
About 80 000 species known, but an estimated 200000+ species extant, mostly
microscopic. Considered the second most diverse animal phylum after the
arthropods.
The Nematoda is a highly diverse group of
free-living or parasitic worms that are difficult to distinguish
from their external appearance because they tend to all have a
uniform worm-like appearance with no external appendages. The
morphological taxonomy of the group has been based on examination of
the internal structures, especially the oesophagus and the male and
female reproductive organs. Life cycle patterns are also important
in distinguishing groups. Molecular phylogenetic anaylysis is
transforming the systematics of the Nematoda, but still has a way to
go before some stability in classification can be attained.
Nematodes are found in abundance in marine,
freshwater and terrestrial habitats. Densities can exceed 1 million
individuals per square metre and it has been claimed that about 80%
of all individual animals on earth are nematodes!
A breakdown of named nematodes (worldwide) by
life style reveals the following distribution of species (from Hugot
et al. 2001).
| Life
style |
No. species |
| Free-living marine |
4070 |
| Free-living terrestrial |
6610 |
| Plant parasites |
4110 |
| Invertebrate parasites |
3500 |
| Vertebrate parasites |
8360 |
| Total |
26650 |
Classification
Based on the
Nematode classification presented on the website of the De Ley Lab,
University of California Riverside.
Enoplea
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Enoplia
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Enoplida
Free-living nematodes that inhabit marine and brackish water where they feed
on algae, diatoms and other similar organisms. |
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Triplonchida
Plant-feeding nematodes. |
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Dorylaimia
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Dorylaimida
Inhabit soil and freshwater. Also includes the family Longidoridae, members
of which are plant parasites and transmit plant viruses. |
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Mononchida
Inhabit soil and freshwater. Predators. |
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Isolaimida
One family: Isolaimidae.
Inhabit soil. |
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Dioctophymatida
Two families: Dioctophymatidae and Soboliphymatidae. |
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Muspiceida
Two families: Muspiceidae and Robertdollfusiidae. |
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Marimermithida
One family: Marimermithidae. |
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Mermithida
Two families: Mermithidae and Tetradonematidae. |
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Trichinellida
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Chromadorea
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Chromadoria
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Desmoscolecida
Three families: Desmoscolecidae, Meyliidae and Cyartonematidae |
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Chromadorida
Five families: Chromadoridae, Ethmolaimidae, Neotonchidae, Achromadoridae
and Cyatholaimidae |
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Desmodorida
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Monhysterida
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Araeolaimida
Four families: Axonolaimidae, Comesomatidae, Diplopeltidae and Coninckiidae |
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Plectida
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Rhabditida
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Uncertain position |
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Benthimermithida
One family: Benthimermithidae. |
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Rhaptothyreida
One family: Rhaptothyreidae. |
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Links
Publications
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Anderson, R.C., 2000. Nematode Parasites of Vertebrates.
Their Development and Transmission, second ed. CABI Publishing, Wallingford,
Oxon.
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Blaxter, M.L., 2003. Nematoda: genes, genomes and the
evolution of parasitism. Advances in Parasitology 54: 102–197.
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Chilton, N.B., Newton, L.A., Beveridge, I., Gasser, R.B.,
2001. Evolutionary relationships of trichostrongyloid nematodes
(Strongylida) inferred from ribosomal DNA sequence data. Molecular
Phylogenetics and Evolution 19: 367–386.
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De Ley, P., Blaxter, M.L., 2002. Systematic position and
phylogeny. In: Lee, D.L. (Ed.), The Biology of Nematodes. Taylor & Francis,
London, pp. 1–30.
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Holterman, M., van der Wurff, A., van den Elsen, S., van
Megen, H., Bongers, T., Holovachov, O., Bakker, J. and Helder, J. 2006.
Phylum-Wide Analysis of SSU rDNA Reveals Deep Phylogenetic Relationships
among Nematodes and Accelerated Evolution toward Crown Clades. Molecular
Biology and Evolution 23(9): 1792-1800.
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Hugot, J-P., Baujard, P. & Morand, S. 2001. Biodiversity in
helminths and nematodes as a field of study: an overview. Nematology, 3:
199-208.
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Liu, J., Poinar, G.O. & Berry, R.E. 2000.
Control of insects pests with entomopathogenic nematodes: the impact of
molecular biology and phylogenetic reconstruction. Annual Review of
Entomology 45: 287-306.
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