What is a Coelom?
A coelom (pronounced “seal-um”) is a fluid-filled body cavity found in most animals. It is located in the mesoderm, the middle germ layer only found in triploblastic (three-layered) organisms. Simpler animals like cnidarians (jellyfish, coral, etc.) and sponges are diploblastic and monoblastic respectively, lacking a coelom. Though the coelom developed in triploblastic animals, some of these animals have lost their coeloms. Animals with a coelom, including the majority of animal phyla, are called coelomates. Animals without a coelom, such as flatworms, are called acoelomates. In between there are some animals called pseudocoelomates, which possess a “false coelom,” which is an unlined or partially lined body cavity between the gut and body wall. A coelom is defined as a cavity that separates the gut from the body wall. The coelom allows the internal organs to shift around and develop independently of the body wall, creating more physiological and evolutionary flexibility. Though the co