The body cavity of animals of the order Nidaria is called a coelenteron. The body cavity of the Hydra is the Cilantron. Archenteron transforms into Cilenteron. It is covered by gastrodermis. It involves extracellular digestion. Food and excreta are transported through it. Hence it is called Gastrovascular cavity. Cilantron is sometimes called blind gut or blind sac. It is exposed through the stoma. Takes food and leaves waste through mouth. Dr. Siddiq Publications