The corallites in which the individual polyps sit are small and crowded and have raised edges or may even be stalked.

There are a large number of fine septa on the edge of the corallites, arranged in whorls and protruding as sharp ridges.

The polyps contain symbiotic protists called zooxanthellae and grow in shallow water to maximise the uptake of sunlight.

[2] They often feed in the day, extending yellowish or greenish, often white tipped tentacles.

[3] They have certain specialised sweeper tentacles, long defensive organs, tipped with powerful cnidocytes which discourage other corals from living close by.