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Secernentea

(Class)

Overview

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Secernentea are the main class of nematodes, characterised by numerous and an excretory system possessing lateral canals. Like all nematodes, they have no circulatory or respiratory system.

The Secernentea contain several significant parasitic species among the Rhabditia and Spiruria. Caenorhabditis elegans, the famous laboratory animal, is one of the many harmless members of the Rhabditia.

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Subclasses and orders of Secernentea are:[1]

Some families traditionally considered to be Rhabditida seem to be closer to the Tylenchida. If the Tylenchia are to be maintained as separate, they probably will be included therein. These are also called as Phasmidians as they have the phasmids which are the posterior glandulo sensory and excretory structure.[1]

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Subclasses and orders of Secernentea are:[1]

Some families traditionally considered to be Rhabditida seem to be closer to the Tylenchida. If the Tylenchia are to be maintained as separate, they probably will be included therein. These are also called as Phasmidians as they have the phasmids which are the posterior glandulo sensory and excretory structure.[1]

References

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  1. ^ a b Tree of Life Web Project (ToL) (2002): Nematoda. Version of January 1, 2002. Retrieved November 2, 2008.

Taxonomy

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The Class Secernentea is a member of the Series Amniota. Here is the complete "parentage" of Secernentea:

The Class Secernentea is further organized into finer groupings including:

Orders

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Aphelenchida

A moderately large order of nematodes. Aphelenchida have a stylet for feeding and a very prominent median bulb in the oesophagus. They are cosmopolitan. Some are associated with insects, and may be ectoparasites or endoparasites, or merely use the insect as transport. Others are associated with plants, as root, stem, or leaf parasites, which may be pathogenic to the plant or not. Still others are associated with fungi, and some are free-living. There may be considerable plasticity of feeding habits within species, involving almost any combination of the categories listed above. Sometimes different feeding habits involve morphologically distinct phases, but they may involve only behavioral differences, and sometimes depend only on the immediate availability of different foods. Some life cycles involve a definite progression of particular hosts and depend on the life cycle of the host. Fungal feeders may have life cycles as short as 5 days. [more]

Ascaridida

The order Ascaridida includes several families of parasitic roundworms with three "lips" on the anterior end. They were formerly placed in the subclass Rhabditia by some, but morphological and DNA sequence data rather unequivocally assigns them to the Spiruria. The Oxyurida and are occasionally placed in the Ascaridida as superfamily Oxyuroidea, but while they seem indeed to be Spiruria, they are not as close to Ascaris as such a treatment would place them. [more]

Camallanida

The Camallanida are an order of nematodes. [more]

Diplogasterida

Diplogasterida is an order of nematodes. It is sometimes placed in a monotypic subclass Diplogasteria, but as it seems it is better included in the Rhabditia. If the Tylenchida are included in the Rhabditia, the Diplogasterida certainly would have to be merged there too [more]

Rhabditida

Rhabditida is an order of free-living, zooparasitic and phytoparasitic matodes (roundworms). [more]

Spirurida

Spirurida is an order of spirurian nematodes. Like all nematodes, they have neither a circulatory nor a respiratory system. [more]

Strongylida

[more]

Tylenchida

Tylenchida is an order of nematodes. [more]

At least 832 species and subspecies belong to the Order Tylenchida.

More info about the Order Tylenchida may be found here.

References

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  1. ^ a b Tree of Life Web Project (ToL) (2002): Nematoda. Version of January 1, 2002. Retrieved November 2, 2008.

Footnotes

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  1. ^ a b ToL (2002)

Sources

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Last Revised: August 24, 2012
2012/08/24 13:06:51