They are radially symmetric, lack a head, possess nematocysts, and have a crown of tentacles around their mouth. This phylum includes such animals as sea anemones, hydras, and jellyfish.
Corals belong to the class Anthozoa.
This means these animals are either solitary or colonial polyps. In addition, Anthozoans live attached to the substrate. The class Anthozoa is further subdivided into three subclasses, two of which are germane to this discussion. The subclass Zoantharia has tentacles in multiples of six. Black corals and reef-building corals belong to this subclass, although they are in different orders.