Dependencies between the Coral Body and the Skeleton

The coral body is made up of a basal and oral discs and walls that create the polyp’s shape. The basal disc forms the bottom of the tubular skeleton, and the walls form the sides. Each place where a coral polyp lives is called a calice. The calice is the distal part of the coral skeleton. One might also hear the term coralite to describe the same term. They are the same, exact thing.

A calice is divided into different chambers by vertical plates called septa. Septa are a part of the skeleton and built from calcium carbonate. Coral septa form radially. This means that the septal plates start at the wall and grow toward the center. Young corals start out with only six septa. This constitutes the first stage in the septal cycle. As each step progresses, the older septum chamber splits to create two new septum chambers. In this way, the number of chambers doubles. The second stage of the septal cycle doubles the existing number of septa and creates six more septa. The total number of septa in the coral is now twelve. The third step of the cycle produces twelve septa for a total of twenty-four. The fourth stage produces twenty-four septa for a total of forty-eight, and so on.

A mesentery is a fleshy septum built of a soft epithelium. Mesenteries are fixed to an oral disk and appear to stream down like curtains dividing coral coelenteron. Digestive filaments and the gonads are attached to the mesenteries that do not connect to the pharynx. The mesentery has gastroderm and mesoglaea. Mesenteries always occur in pairs. Skeletal septa are as cyclical in arrangement as mesenteries There is usually one septum between two paired mesenteries. The first septal cycle appears before the first cycle of mesenterial pairs do.