Black coral is colonial with a rigid, rod-like skeleton forming large aborescent fans that are dark brown to almost black in colour. There are no calcareous components in the skeleton, and no calcareous spines (spicules or sclerites) in the soft tissues, home to the large polyps (up to 3cm). Each polyp has a circle of numerous smooth tentacles. Both the colony and the polyps are yellow.
Though capable of forming its own skeleton, this species usually covers that of the Gorgonians. The invasion takes place on both living and dead colonies, which are progressively destroyed by the Gerardia as it grows up to 8 cm per year. Recently an association has been discovered between this species and the Balsia Gasti Shrimp.