Sea fans or also often called gorgonians are colonial marine animal forming erect, flattened, branching colonies in tropical and subtropical waters. They have a central internal skeleton, composed of a flexible, horny substance called „gorgonin“, supports all branches of the colony, and the living tissues form a layer over its entire surface. Colonies may be several feet high and are most often colorful, with purples, reds, and yellows predominating. Cylindrical sessile forms—that grow together in a flat, fanlike pattern. The individuals, or polyps, have six or eight feathery tentacles and feed on plankton organisms.