- an aquatic invertebrate animal of a phylum that includes jellyfishes, corals, and sea anemones. They are distinguished by having a tube- or cup-shaped body and a single opening ringed with tentacles. Also called cnidarian.
- Phylum Cnidaria (formerly Coelenterata): four classes
late 19th century: from modern Latin Coelenterata, from Greek koilos 'hollow' + enteron 'intestine'