Coelom

The coelom (/ˈsiːləm/ SEE-ləm, plural coeloms or coelomata /siːˈloʊmətə/ see-LOH-mə-tə) (Greek koilōma, hollow, cavity) refers to the main body cavity in most multicellular animals and is positioned inside the body to surround and contain the digestive tract and other organs. In developed animals, it is lined with a mesodermal epithelium. In other animals, such as molluscs, it remains undifferentiated.

Structure

Development

Coelom formation begins in the gastrula stage. The developing digestive tube of an embryo forms as a blind pouch called the archenteron.

In Protostomes the coelom forms by a process known as schizocoely. The archenteron initially forms, and the mesoderm splits into two layers: the first attaches to the body wall or ectoderm, forming the parietal layer and the second surrounds the endoderm or alimentary canal forming the visceral layer. The space between the parietal layer and the visceral layer is known as the coelom or body cavity.

In Deuterostomes, the coelom forms by enterocoely: mesoderm buds from the walls of the archenteron and hollows to become the coelomic cavities.