Polyp, in zoology, a tubelike water animal. Most polyps are marine animals, but a few kinds live in freshwater. A polyp has a closed end, the foot, by which the animal attaches itself to an object such as a rock, seaweed, or another polyp. The other end, unattached, has an opening, the mouth, that is typically fringed by numerous tentacles.
Most polyps belong to the classes Hydrozoa and Anthozoa of the phylum Cnidaria.