SYNOPTIC DESCRIPTION OF THE PHYLUM XENOTURBELLIDA

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PHYLUM XENOTURBELLIDA LINKS

Hierarchical Classification

The following description of the phylum Xenoturbellida came from Bourlat et al. (2006), Brusca and Brusca (2003), Nielsen (2001), Pechenik (2005), Swalla and Smith (2008) and Telford (2008).

I. SYNONYMS: acoels, flatworms.

II. NUMBER: 2

III. PHYLUM CHARACTERISTICS:
- A. Structure
  - Symmetry: Bilateral.
  - Body Cavity: No coelom.
  - Body Covering: Covered by ciliated epithelium.
  - Support: Hydrostatic?
  - Digestive System: Very simple. Ventral mouth and blind gut without pharynx.
  - Circulatory System: Absent.
  - Locomotion: Crawl over substrate with ciliated epithelium.
  - Excretory System: Absent.
  - Nervous System: Simple anterior-posterior nerves, more like a nerve net. Have an anterior statocyst (sensory organ?).
  - Endocrine System:
  - Respiratory System: Absorption through epidermis.
- B. Reproduction:
  - Reproductive System: Little is known. Hermaphroditic?
  - Development: Spiral cleavage reported.
- C. Ecology: Benthic marine flatworms at sites in the North Sea 20-100 m deep.

LITERATURE CITED

Bourlat, S. J., 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, and M. J. Telford. 2006. Deuterostome phylogeny reveals chordates and the new phylum Xenoturbellida. Nature. 444: 85-88.

Brusca, R. C. and G. J. Brusca. 2003. Invertebrates. Sinauer Associates, Inc. Sunderland, Mass.

Nielsen, C. 2001. Animal Evolution: Interrelationships of the Living Phyla. 2nd Edition. Oxford University Press. Oxford.

Pechenik, J. A. 2005. Biology of the Invertebrates. McGraw-Hill. New York.

Swalla, B. J. and A. Smith. 2008. Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives. Phil. Trans. R. Soc. B. 363:1557-1568.

Telford, M. J. 2008. Xenoturbellida: the fourth deuterostome phylum and the diet of worms. Genesis. 46: 580-586.

By Jack R. Holt and Carlos A. Iudica. Last revised: 01/26/2011

SYNOPTIC DESCRIPTION OF THE PHYLUM XENOTURBELLIDA

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