Septum (coral)

In coral anatomy, a septum (plural: septa) is one of the radial, vertical plates found within the corallite, the skeletal cup that houses a coral polyp. These plate-like structures project inward from the wall of the corallite (the theca) towards the center, or axis, of the polyp. Septa provide support for the soft tissues of the coral polyp, specifically the mesenteries, which are internal partitions that extend from the body wall to the pharynx and contain digestive filaments.

The arrangement and morphology of the septa are important characteristics used in the identification and classification of coral species. The number, shape, and ornamentation (such as teeth or granules) on the septa can vary greatly between different coral taxa. The septa are formed by the coral polyp through the deposition of calcium carbonate (aragonite).

The arrangement of septa is generally radial, meaning they extend outwards from the center like spokes on a wheel. They may be arranged in a specific pattern, such as cycles, where each cycle consists of a series of septa of progressively smaller size. The first cycle of septa to develop are the primary septa, followed by secondary, tertiary, and so on. The arrangement and number of cycles are often consistent within a species.

The septa contribute significantly to the overall strength and rigidity of the coral skeleton, helping the coral withstand physical forces and providing a framework for tissue growth and expansion.