What phylum includes jellyfish, corals, and sea anemones?

Jellyfish, corals, and sea anemones belong to the phylum Cnidaria.

Cnidarians are aquatic invertebrates named for their cnidocytes, specialized stinging cells used to capture prey and deter predators. These cells contain microscopic structures that can discharge venomous threads. Although their bodies look very different, a drifting jellyfish, a stationary sea anemone, and a coral colony share this distinctive biological equipment.

Many cnidarians alternate between two basic body forms: the swimming medusa and the attached polyp. Jellyfish are chiefly associated with the medusa form, while sea anemones remain polyps. Corals are also polyp-form animals, often living in colonies whose skeletons accumulate into reefs. Cnidarians generally have radial symmetry, a nerve net rather than a centralized brain, and a digestive cavity with a single opening.

Cnidaria is sometimes confused with Ctenophora, the phylum of comb jellies. Older classifications grouped them together under Coelenterata, but comb jellies lack cnidarian stinging cells and are now treated as a separate phylum.