Koilenteron

Koilenteron, also spelled coelenteron, is the gastrovascular cavity of cnidarians (the phylum that includes jellyfish, corals, and sea anemones). The term derives from Greek roots meaning hollow intestine. It is the primary body cavity in these animals and is not a true coelom.

In cnidarians, the koilenteron is a single, blind-ending sac that opens to the exterior through the mouth. Its internal lining is the gastrodermis. Depending on the group, the cavity may be subdivided by mesenteries or linked by radial and ring canals. In hydrozoans, the cavity typically includes a central stomach with radial canals connected to a ring canal; in anthozoans, the cavity is more extensively partitioned by numerous mesenteries, forming multiple gastric compartments; in many medusae, the cavity includes a central stomach with a network of radial canals that distribute nutrients.

Functionally, the koilenteron serves both digestion and circulation. Digestive enzymes released into the cavity perform extracellular digestion of prey, and the resulting nutrients are absorbed by gastrodermal cells. The cavity also helps distribute nutrients and gases through the fluid within, and it provides a hydrostatic skeleton that supports the animal's shape and movement.

The koilenteron is characteristic of cnidarians and reflects their diploblastic organization and lack of a true coelom. In some literature, it is equated with the coelenteron, the more common term used in English texts. See also coelenterates, gastrovascular cavity.