The Chromadorea are a class of the roundworm phylum,
Nematoda
The nematodes ( or ; ; ), roundworms or eelworms constitute the phylum Nematoda. Species in the phylum inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitism, parasitic. Parasitic ...
. They contain a single
subclass (Chromadoria) and several orders. With such a redundant arrangement, the Chromadoria are liable to be divided if the orders are found to form several
clade
In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
s, or abandoned if they are found to constitute a single radiation.
Formerly, they were treated as a subclass in the
paraphyletic
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
"
Adenophorea" assemblage, which has been mostly abandoned by modern authors. It is also suspected that the Chromadorea may not be
monophyletic
In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria:
# the grouping contains its own most recent co ...
as delimited here; at least the
Monhysterida seem to be a distinct and far more ancient lineage than the rest.
Members of this class' bodies usually have annules, their
amphids elaborate and spiral, and they all have three
esophageal glands. They usually live in marine sediments, although they can live elsewhere. They have a more sophisticated
pharynx
The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...
than most roundworms.
Members of this class can be identified by the presence of eight
conserved signature indels (CSIs) exclusively shared by the class.
These molecular markers are found in essential proteins such as
tRNA (guanine-N(1))-methyltransferase and can serve as a reliable molecular method of distinguishing the Chromadorea from other classes within the phylum Nematoda.
Orders
Provisionally, the following orders are placed here:
*
Araeolaimida
*
Ascaridida
*
Chromadorida
*
Desmodorida
*
Desmoscolecida
*
Monhysterida
*
Rhabditida
*
Rhigonematida
Notes
The
Benthimermithida are also occasionally placed here.
The Ascaridida appear to be nested within Rhabditida.
References
External links
* (2002)
Nematoda Version of 2002-JAN-01. Retrieved 2008-NOV-02.
Ecdysozoa classes
{{Chromadorea-stub