Xenoturbella
| Xenoturbella | |
|---|---|
Scientific classification  |
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| Kingdom: | Animalia |
| Superphylum: | Deuterostomia (?) |
| Phylum: | Xenoturbellida |
| Family: | Xenoturbellidae |
| Genus: | Xenoturbella |
| Species | |
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Xenoturbella is a genus of bilaterian animals; it contains two marine worm-like species. The first known species (Xenoturbella bocki) was discovered in 1915 by Sixten Bock but the first published description was only in 1949 by Einar Westblad.[1] Its taxonomic position has been considered enigmatic since its discovery 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,[2][3] and allied with the acoelomorpha, forming a sister clade to the echinoderms and hemichordates.[4]
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 centimetres (1.6 in) long, and has been found off the coasts of Sweden, Scotland and Iceland.[5]
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 the Xenoturbella larval stage develops as an internal parasite of certain molluscs.[6]
The genus Xenoturbella contains two species:
[edit] Notes
- ^ Westblad (1949) Arkiv. Zoologi. 1:3-29
- ^ 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 [1]
- ^ Telford, M. J. (2008). "Xenoturbellida: the fourth deuterostome phylum and the diet of worms". Genesis 46 (11): 580–586. doi:10.1002/dvg.20414. PMID 18821586.
- ^ Philippe, H.; Brinkmann, H.; Copley, R. R.; Moroz, L. L.; Nakano, H.; Poustka, A. J.; Wallberg, A.; Peterson, K. J. et al (2011). "Acoelomorph flatworms are deuterostomes related to Xenoturbella". Nature 470 (7333): 255-258. Bibcode 2011Natur.470..255P. doi:10.1038/nature09676.
- ^ Enigmatic worm identified as mankind's long lost relative – Accessed January 3, 2008
- ^ Xenoturbella – Back to the Basics – Accessed January 3, 2008
[edit] References
- E. Westblad (1949). "Xenoturbella bocki n.g., n.sp., a peculiar, primitive turbellarian type". Arkiv för Zoologi 1: 3–29.
- 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
- M. Noren, U. Jondelius (1997). "Xenoturbella's molluscan relatives..". Nature 390 (6655): 31–32. doi:10.1038/36242.
- O. Israelsson (1999). "New light on the enigmatic Xenoturbella (phylum uncertain): ontogeny and phylogeny". Proc. Roy. Soc. B 266 (1421): 835–841. doi:10.1098/rspb.1999.0713.
- O. Israelsson O, G. E. Budd G E (2006). "Eggs and embryos in Xenoturbella (phylum uncertain) are not ingested prey". Development Genes and Evolution 215 (7): 358–363. doi:10.1007/s00427-005-0485-x. PMID 15818482.
- S. J. Bourlat, C. Nielsen, A. E. Lockyer, D. Timothy, J. Littlewood, M. J. Telford (2003). "Xenoturbella is a deuterostome that eats molluscs". Nature 424 (6951): 925–928. doi:10.1038/nature01851. PMID 12931184. [2]
- S. J. Bourlat, T. Juliusdottir, C. J. Lowe, R. Freeman, J. Aronowicz, M. Kirschner, E. S. Lander, M. Thorndyke, H. Nakano, A. B. Kohn, A. Heyland, L. L. Moroz, R. R. Copley, M. J. Telford (2006). "Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida". Nature 444 (7115): 85–88. doi:10.1038/nature05241. PMID 17051155.
- Olle Israelsson, Graham E Budd (2005). "Eggs and embryos in Xenoturbella (phylum uncertain) are not ingested prey". Development Genes and Evolution 215: 358-63 [3]
- K. U. Kjeldsen, M. Obst, H. Nakano, P. Funch, A. Schramm (2010). "Two Types of Endosymbiotic Bacteria in the Enigmatic Marine Worm Xenoturbella bocki". Applied and Environmental Microbiology 76 (8): 2657–2662. doi:10.1128/aem.01092-09. PMC 2849209. PMID 20139320. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2849209.
[edit] External links
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