The coelom ( /ˈsiːləm/ SEE-ləm) (also celom) is a fluid-filled cavity formed within the mesoderm of some animals. 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.
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. In mammals, the coelom forms the peritoneal, pleural, and pericardial cavities.
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 was 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. The coelomate phyla comprise Entoprocta, Ectoprocta, Phoronida, Brachiopoda, Mollusca, Priapulida, Sipuncula, Echiura, Annelida, Tardigrada, Pentastoma, Onychophora, Arthropoda, Pogonophora, Echinodermata, Chaetognatha, Hemichordata and Chordata.
Other articles related to "coelom, coeloms":
... development of digestive system, coelom and septa, and mesenchymal mesenteric masses (GA 11.1101, TE E5.4, 5.8-9) Gut Upper GI tract and accessory Stomodeum Foregut ...
... mesoderm is formed in a developing embryo, in which the coelom forms from pouches "pinched" off of the digestive tract (also known as the embryonic gut ... This type of coelom formation occurs in deuterostome animals, which for this reason are also known as enterocoelomates ... This then leads to the formation of a coelom ...
... glomerulus (or glomus if it extends over multiple body segments) projects into the coelom rather than into the proximal tip of the nephron ... The glomerular filtrate flows directly into the coelom, or a dorsal compartment of the coelom known as the nephrocoel ...
... Most annelids have a pair of coeloms (body cavities) in each segment, separated from other segments by septa and from each other by vertical mesenteries ... that the mesothelium is the lining of each of the pair of coeloms, and the blood vessels and, in polychaetes, the main nerve cords are embedded in it ... The fluid in the coeloms contains coelomocyte cells that defend the animals against parasites and infections ...