The sedentary stage in the life cycle of the Cnidaria, consisting of a cylindrical body fixed at one end to a firm base and having a mouth surrounded by a ring of tentacles at the other. Some polyps (e.g. Hydra) are single; others (e.g. the corals and Obelia) form colonies. Polyps typically reproduce asexually by budding to form either new polyps or medusae. The latter reproduce sexually giving rise to new polyps. Sea anemones are solitary polyps that reproduce sexually to form new polyps.