Xenoturbella

Taxobox | name = "Xenoturbella"


regnum = Animalia
unranked_phylum = Bilateria
superphylum = Deuterostomia
phylum = Xenoturbellida
familia = Xenoturbellidae
genus = "Xenoturbella"
subdivision_ranks = Species
subdivision = "X. bocki" Westblad, 1949 "X. westbladi" Israelsson, 1999

"Xenoturbella" is a genus of bilaterian animals; it contains two marine worm-like species. Its taxonomic position has been considered enigmatic since its discovery in 1949, but a 2003 DNA study has positioned it as a primitive deuterostome outside the established phyla (Bourlat "et al.", 2003). Earlier it was suspected to be closely related to molluscs (Noren & Jondelius, 1997), but it turned out that the DNA test was contaminated with DNA from molluscs which it may have eaten (Bourlat "et al.", 2003; Israelsson & Budd, 2006). The earlier results were recently corroborated; the genus is now the sole member of its own phylum Xenoturbellida (Haszprunar "et al.", 1991; Bourlat "et al.", 2006). It appears that this phylum is basal within the deuterostomes.Perseke M, Hankeln T, Weich B, Fritzsch G, Stadler PF, Israelsson O, Bernhard D, Schlegel M. (2007) "The mitochondrial DNA of "Xenoturbella bocki": genomic architecture and phylogenetic analysis". "Theory Biosci". 126(1):35-42. Available on-line at [http://www.bioinf.uni-leipzig.de/Publications/PREPRINTS/07-009.pdf] ]

"Xenoturbella" has a very simple body plan: it has no brain, no through gut, no excretory system, no organized gonads (but does have gametes; eggs and embryos occur in follicles [Israelsson and Budd] ), or any other defined organs except for a "statocyst" containing flagellated cells; it has cilia and a diffuse nervous system. The animal is up to 4 cm long, and has been found off the coasts of Sweden, Scotland and Iceland. [ [http://www.wellcome.ac.uk/doc_WTD002847.html Enigmatic worm identified as mankind's long lost relative] - Accessed January 3, 2008]

The association of specimens of "Xenoturbella" with mollusc larva has led many to suggest that they are molluscivores. However, a more radical interpretation, of this and other data, is that that the "Xenoturbella" larval stage develops as an internal parasite of certain molluscus. [ [http://www.palaeos.com/Invertebrates/Deuterostomia/80A000Ambulacraria.html#Xenoturbella "Xenoturbella" - Back to the Basics] - Accessed January 3, 2008]

The genus "Xenoturbella" contains two species:
* "Xenoturbella bocki"
* "Xenoturbella westbladi"

Notes

References

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* G. Haszprunar, R.M. Rieger, P. Schuchert (1991). "Extant 'Problematica' within or near the Metazoa." In: Simonetta, A.M. & Conway Morris, S. (eds.): "The Early Evolution of Metazoa and the Significance of Problematic Taxa". Oxford Univ. Press, Cambridge. pp. 99-105
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* [http://www.nature.com/nature/journal/v424/n6951/abs/nature01851_fs.html]
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* Olle Israelsson, Graham E Budd (2005). "Eggs and embryos in "Xenoturbella" (phylum uncertain) are not ingested prey". Development Genes and Evolution 215: 358-63 [http://lib.bioinfo.pl/pmid:15818482]

External links

* [http://www.bioinf.uni-leipzig.de/Publications/PREPRINTS/07-012.pdf A PCR Survey of Xenoturbella bocki Hox Genes]