Ecdysozoa

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(Redirected from Cycloneuralia)

{{Taxobox | color = pink | name = Ecdysozoa | image = Centipede.jpg | image_width = 225px | image_caption = Centipede | regnum = Animalia | subregnum = Eumetazoa | unranked_phylum = Bilateria | superphylum = Ecdysozoa | superphylum_authority = Aguinaldo et al., 1997 | subdivision_ranks = Phyla | subdivision = Panarthropoda
  Arthropoda
  Onychophora
  Tardigrada
Scalidophora
  Kinorhyncha
  Priapulida
  Loricifera
Nematoda
Nematomorpha }}

The Ecdysozoa are a group of protostome animals, including the Arthropoda, Nematoda, and several smaller phyla. They were first defined by Aguinaldo et al. in 1997, based mainly on trees constructed using 18S ribosomal RNA genes. However, the group is also strongly supported by morphological characters, and can be considered as including all animals that shed their exoskeleton (see ecdysis). Groups corresponding roughly to the Ecdysozoa had been proposed previously by Perrier in 1897 and Seurat in 1920 based on morphology alone.

The most notable characteristic shared by ecdysozoans is a three-layered cuticle composed of organic material, which is periodically molted as the animal grows. This process is called ecdysis and gives the group its name. Ecdysozoans lack locomotory cilia, produce amoeboid sperm, and their embryos do not undergo spiral cleavage as in most other protostomes. Various other features are found in the group - for instance, both tardigrades and roundworms have a triradiate pharynx.

The Ecdysozoa include the following phyla: Arthropoda, Onychophora, Tardigrada, Kinorhyncha, Priapulida, Loricifera, Nematoda and Nematomorpha. A few other groups, such as the gastrotrichs, have been considered possible members but lack the main characters of the group, and are now placed elsewhere. The Panarthropoda are distinguished by a segmented body plan, and as such were traditionally believed to have evolved from the Annelida (segmented worms), together comprising the Articulata. However, they do not have many other characteristics in common, so it now appears that they developed segmentation separately.

The non-panarthropod members of Ecdysozoa have been grouped as Cycloneuralia but they are more usually considered paraphyletic.

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References

  • Aguinaldo, A. M. A., J. M. Turbeville, L. S. Linford, M. C. Rivera, J. R. Garey, R. A. Raff, & J. A. Lake, 1997. Evidence for a clade of nematodes, arthropods and other moulting animals. Nature 387: 489-493.
  • Wagele, J. W., T. Erikson, P. Lockhart, & B. Misof, 1999. The Ecdysozoa: Artifact or monophylum? J. Zoo. Syst. Evol. Research 37: 211-223.
  • Tree of Life web project - Bilateria - accessed January 8 2006
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External links

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