coelomic

Coelomic refers to the coelom, the primary fluid-filled body cavity in many multicellular animals. The coelom is lined by a mesoderm-derived tissue known as the coelomic epithelium or peritoneum and contains coelomic fluid. It forms during embryonic development by processes called schizocoely or enterocoely, creating a distinct space between the body wall and the gut.

Organized into coelomates, animals possess a true coelom; acoelomates lack a separate body cavity, while pseudocoelomates have a cavity that is not fully lined by mesoderm. The presence or absence of a coelom is a fundamental feature in animal classification and correlates with patterns of development and organ arrangement.

The coelom serves multiple roles. It provides a mechanical hydrostatic skeleton that supports movement, offers space for the growth and independent movement of internal organs, and acts as a medium for distribution of nutrients, wastes, and other substances. In many groups, the coelomic fluid also participates in diffusion and immune functions and helps cushion organs.

In vertebrates and other chordates, the coelom is partitioned into specialized cavities such as the pericardial cavity, pleural cavities, and the peritoneal cavity, all lined by mesothelium. The lining of these spaces and their associated membranes—collectively part of the coelomic system—contribute to serous membranes and fluid regulation throughout the body.

Typical examples of organisms with a well-defined coelom include annelids, mollusks, echinoderms, and chordates. The term coelomic emphasizes both the cavity itself and its lining, which share a common developmental and functional heritage.