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A coelomate animal is basically a set of concentric tubes, with a gap between the gut and the outer tubes.

The coelom (/ˈsləm/ SEE-ləm, plural coeloms or coelomata /sˈlmətə/ see-LOH-mə-tə) (also celom, -s) (Greek koiloma, cavity) is a fluid-filled body cavity between the intestines and the body wall of some higher metazoans. It is lined with a mesodermal epithelium. The coelom is formed within the mesoderm of the embryo. In mammals, the coelom then develops into the peritoneal, pleural, and pericardial cavities. In other animals, e.g., molluscs, it remains undifferentiated.


Functionally, a coelom can absorb shock or provide a hydrostatic skeleton. It also allows muscles to grow independently off the body wall. This can be seen in the digestive tract of water bears and other tardigrades, which is suspended within the body in a mesentery derived from a mesoderm-lined coelom.

Biology and zoology[edit]

Coeloms developed in diploblasts but were subsequently lost in several lineages. Loss of coelom is correlated with reduction in body size. Coelom is sometimes (incorrectly) used to refer to any developed digestive tract. Some organisms may not possess a coelom or may have a false coelom (pseudocoelom). Animals having coelomata are called coelomates.

In the past, zoologists grouped animals based on characteristics related to the coelom. The presence or absence of a coelom and the way in which it was formed were believed to be important in understanding the phylogenetic relationships of animal phyla. However, recent molecular phylogenies have suggested this characteristic is not as informative as previously believed: the coelom may have arisen twice, once in protostomes and once among the deuterostomes.[1] The coelomate phyla comprise Entoprocta, Ectoprocta, Phoronida, Brachiopoda, Mollusca, Priapulida, Sipuncula, Echiura, Annelida, Tardigrada, Pentastoma, Onychophora, Arthropoda, Pogonophora, Echinodermata, Chaetognatha, Hemichordata and Chordata (i.e., from tiny sessile aquatic animals to humans and everything in between).[2]

See also[edit]


  1. ^ Xiao, S.; Laflamme, M. (2008). "On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota". Trends in Ecology & Evolution 24 (1): 31–40. doi:10.1016/j.tree.2008.07.015. PMID 18952316 
  2. ^ "Coeloms and Pseudocoeloms". Retrieved August 30, 2011. 

Further reading[edit]