Acoela
Top
(ā′sēl·ə)
(invertebrate zoology) An order of marine flatworms in the class Turbellaria characterized by the lack of a digestive tract and coelomic cavity.
An order of marine Turbellaria, generally regarded as primitive, and lacking protonephridia, oviducts, yolk glands, permanent digestive cavity, and strictly delimited gonads. The nervous system is epidermal in the most primitive representatives, but it is generally submuscular and consists of three to six pairs of longitudinal strands without anterior concentrations recognizable as a brain. The anterior or median ventral mouth opens into a simple pharynx which lacks elaborate musculature and leads directly to the syncytial vacuolated mass of endoderm forming the spongy intestinal tissue and lacking any true lumen.
Eyes are often absent; when present they are of the usual paired turbellarian pigment-cup type, with one to a few pigment and retinal cells. The epidermis, typically, is uniformly ciliated, and locomotion is accomplished by means of rapid, smooth ciliary gliding or swimming.
The acoels (see illustration) are mostly small (one to several millimeters in length). They are virtually worldwide in distribution, living beneath stones, among algae, on the bottom mud, or interstitially, from the littoral zone to deeper waters. A few are pelagic (in tropical and subtropical zones), and others have become symbiotic, living entocommensally in various invertebrates but mainly in echinoderms. See also Coelenterata; Platyhelminthes; Turbellaria.
Acoela: Childia spinosa.
Wikipedia on Answers.com:
Top
Acoela
| Acoela | |
|---|---|
 |
|
| Flatworm-like Waminoa sp. on Plerogyra sp. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Subkingdom: | Metazoa |
| Phylum: | Acoelomorpha |
| Class: | Acoela |
| Order: | not assigned |
| Families | |
Acoela is an order of animals treated either as a group of flatworms[1] or as one of the two classes of the phylum Acoelomorpha, containing the majority of that phylum's species. It contains about 20 families.
As the most primitive bilateral animals, Acoela provide interesting insights into early animal evolution and development.[2][3] The best studied animal in this group is the European species Symsagittifera roscoffensis.
References
- ^ Jimenez-Guri E, Paps J, Garcia-Fernandez J, Salo E (2006), "Hox and ParaHox genes in Nemertodermatida, a basal bilaterian clade", Int. J. Dev. Biol. 50 (8): 675–9, doi:10.1387/ijdb.062167ej, PMID 17051477, http://www.intjdevbiol.com/paper.php?doi=10.1387/ijdb.062167ej.
- ^ Hejnol A, Martindale MQ (2008), "Acoel development supports a simple planula-like urbilaterian", Phil. Trans. R. Soc. B 363 (1496): 1493–1501, doi:10.1098/rstb.2007.2239, , PMID 18192185
- ^ Hejnol A, Martindale MQ (2008), "Acoel development indicates the independent evolution of the bilaterian mouth and anus", Nature 456 (7220): 382, doi:10.1038/nature07309, PMID 18806777
 |
Wikimedia Commons has media related to: Acoela |
 |
Wikispecies has information related to: Acoela |
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Post a question - any question - to the WikiAnswers community:
Copyrights:
McGraw-Hill Science & Technology Dictionary
McGraw-Hill Dictionary of Scientific and Technical Terms. Copyright © 2003, 1994, 1989, 1984, 1978, 1976, 1974 by McGraw-Hill Companies, Inc. All rights reserved.
Read more
McGraw-Hill Science & Technology Encyclopedia
McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved.
Read more
