Gourt > Science > Biology > Genetics > Eukaryotic > Animal > Nematodes
The nematodes or roundworms (Phylum Nematoda from Gr. nema, nematos "thread" + ode "like") are one of the most common phyla of animals, with over 20,000 different described species (over 15,000 are parasitic). They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as Antarctica and oceanic trenches. Further, there are a great many parasitic forms, including pathogens in most plants and animals, humans included. Only the Arthropoda are more diverse.
The Nematodes were originally named Nematoidea by Rudolphi (1808). They were renamed Nematodes by Burmeister 1837 (as a family; Leuckart 1848 and von Siebold 1848 both promoted them to the rank of order), then Nematoda (Diesing 1861), though Nathan Cobb (1919) argued that they should be called Nemata or Nemates (and in English 'nemas' rather than 'nematodes'). After some confusion which saw the nematodes placed (often together with the horsehair worms, Nematomorpha) as a class or order in various groups such as Aschelminthes, Lankester (1877) definitively promoted them to the level of phylum.
Morphology
Nematodes are triploblastic protostomes with a complete digestive system. Roundworms have no circulatory or respiratory systems so they use diffusion to breathe and for circulation of substances around their body. They are thin and are round in cross section, though they are actually bilaterally symmetric. Nematodes are one of the simplest animal groups to have a complete digestive system, with a separate orifice for food intake and waste excretion, a pattern followed by all subsequent, more complex animals. The body cavity is a pseudocoel (persistent blastula), which lacks the muscles of coelomate animals used to force food down the digestive tract. Nematodes thus depend on internal/external pressures and body movement to move food through their digestive tracts. The mouth is often surrounded by various flaps or projections used in feeding and sensation. The portion of the body past the anus or cloaca is called the "tail." The epidermis secretes a layered cuticle made of keratin that protects the body from drying out, from digestive juices, or from other harsh environments, as well as in some forms sporting projections such as cilia that aid in locomotion. Although this cuticle allows movement and shape changes via a hydrostatic skeletal system, it is very inelastic so does not allow the volume of the worm to increase. Therefore, as the worm grows, it has to moult and form new cuticles. The cuticles don't allow volume to increase so as to keep hydrostatic pressure inside the organism very high. For this reason, the roundworms do not possess circular muscles (just longitudinal ones) as they're not required. This hydrostatic pressure is the reason the roundworms are round. More on [ Nematode ]
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Blaxter Lab Nematode Genomics - Features sequencing data, evolution and development, phylogenetics, and links to filarial data. Includes a genetics course, research techniques and references.
500
Blaxter Lab Nematode Genomics - Sequence expressed sequence tags from parasitic nematode species to identify new drug and vaccine targets. Includes an experimental cluster database searchable by both annotation and sequence homology.
Caenorhabditis Elegans Network - Provides navigation to information and data on a range of topics including genetics, bioinformatics, aging, and oxidative stress.
Meta Description: [ Comprehensive index of model organism informatics,
functional genomics, services, tools, databases,
career, tutorials, protocols, meetings ]
Caenorhabditis Elegans WWW Server - Offers genome data, features an introduction to the field, a list of worm labs, literature, meeting announcements and software.
404
Caenorhabditis Genetics Center - Coordinate and maintain a range of data. Includes databases and maps, bibliography, nomenclature, and a strain list.
Nematode Net - Project at Washington University to sequence parasitic nematodes of humans, animals, and plants. Provides access to new gene sequence information, tools for analyzing nematode sequences, and brief information and photos of the species.
Meta Description: [ Nematode genomics. The GSC, at
Washington University St. Louis, is sequencing 235,000 ESTs from
parasitic nematodes of humans, animals, and plants. Nematode.Net
provides easy access to new gene sequence information and other tools
for analyzing nematode sequences. ]
Vanfleteren Lab - Research at Ghent University, Belgium, including ageing , molecular phylogeny of nematodes, and Globins: structure-function relationships.
Wheaton Genomics Research Group - A collection of search and visualization tools for regulatory sites in intergenic regions of the organism C.elegans, including a motif lexicon.
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