Cnidarian, ny DAIR ee uhn, is the name of a group of soft-bodied water animals. The group includes the freshwater hydras, hydroids, jellyfish, sea fans, sea anemones, and corals. These animals make up the phylum (large group) called Cnidaria. There are approximately 9,000 species of cnidarians, and most of them live in the sea. Cnidarians are also called coelenterates.