The first thing to know about this animal phylum is that the "c" that begins "Cnidaria" is silent. Thus, the proper phonetic pronunciation of the group is "ni-daria."

Modern cnidarians exhibit a great diversity of forms, all of which are aquatic and most of which are marine. Cnidaria includes all ancient and modern corals, sea anemones, jellyfish, as well as a variety of less well-known groups.

All cnidarians have share features in common.