coelom A fluid-filled (see COELOMIC FLUID) body cavity that originates by the splitting of the mesoderm of triploblastic animals. It separates the muscles of the body wall from the gut, allowing them to move independently, and provides an area for the enlargement of internal organs, thus permitting the gut to be differentiated for various functions. In many animals, the coelom plays an important part in collecting excretions and acts as a storage site for the maturation of gametes. It is well developed in Vertebrata, Echinodermata, and Annelida, but in Arthropoda and Mollusca it is reduced and its role replaced by the haemocoel.

coelom A fluid-filled cavity that forms the main body cavity of vertebrate and most invertebrate animals. It is formed by the splitting of the mesoderm. Ciliated ducts (coelomoducts) connect the coelom to the exterior allowing the exit of waste products and gametes; in higher animals these are specialized as oviducts, etc. The coelom is large and often subdivided in annelid worms (in which it functions as a hydrostatic skeleton) and vertebrates. In arthropods it is restricted to the cavities of the gonads and excretory organs, the body cavity being a blood-filled haemocoel.

coelom Principal body cavity in most animals, forming the cavity around the gut in many Annelida, and in Echinodermata and Vertebrata. In Arthropoda and Mollusca, the main body cavity is an expanded part of the blood system (a haemocoel) and the coelom is small.