One example of the phylum Cnidaria is coral. Cnidaria is an extremely diverse group of aquatic creatures, some of which swim freely through the ocean, and some of which, such as coral, appear more like plants than animals. Like starfish, cnidarians have radial body plans.
Coral are tiny, soft-bodied animals. They somewhat resemble upended jellyfish, with tentacles surrounding their only orifice, which serves as both anus and mouth. The coral reef is not the animal itself but a structure built by many coral together. The creatures take in calcium from seawater and convert it into a protective coating that they secrete around themselves. The resemblance to jellyfish is not a coincidence; coral is related to box jellies and the true jellyfish. Some cnidarians switch between a stationary, coral-like form and a free-swimming, jellyfish form over the course of their life cycle.