Red Coral belongs to a large relatively primitive zoological branch, the Cnidaria. This branch is polymorphic and groups animals as different as jellyfish, freshwater hydra, reef-building corals, sea anemones, black coral, gorgonian…all of which are united by their possession of cnidocytes.
Although the name 'coral' was originally given to red coral, it was also given later to several different genera: black coral (Antipathes, with a non-mineral, horny skeleton), reef building corals Scleractinaria, with an aragonite skeleton), blue coral, soft coral …. But whereas the reef-building corals need light to live and elaborate their imposing skeleton, the red coral prefers shade. Also, its rate of calcification is slight: several millimetres a year, compared with several centimetres for tropical coral!