corallite

A corallite is the skeletal cup formed by an individual coral polyp and housing the polyp within a colony. In most stony corals, each polyp resides in its own corallite, a cup-shaped chamber bounded by thecal walls that constitute the outer skeleton.

Structure and components: The walls of a corallite are the thecae. Inside, radial septa extend inward from the thecal walls toward the center, and in many species additional lateral elements called costae reinforce the structure. The central area may contain a columella, a small vertical pillar of calcareous material. The polyp extends its tentacles and mouth through the opening at the top of the corallite, known as the calyx.

Variations and biology: Solitary corals consist of a single corallite, while colonial corals form many corallites that can be closely spaced or individually separated by thin walls. Corallites can vary in size, shape, and the arrangement of septa and costae, and these features are often used to identify species and determine growth forms. In many modern corals, the skeleton is primarily aragonite, though composition can vary among groups and through geological time.

Fossil significance: Corallite morphology is a key taxonomic character in fossil corals, including rugose and tabulate forms, where size, shape, and the pattern of septa and walls help distinguish lineages and infer paleoecology and paleoenvironments.

See also: coral skeleton, calyx, theca, septa, costae, columella.