In zoology, a polyp is one of two forms of inividuals found in many species of cnidarians. The two are the polyp or hydroid and the medusa. Polyps are approximately cylindrical, elongated on the axis of the body. The aboral end is attached either to the substrate by means of a disc-like holdfast if the polyp is solitary, or is connected to other polyps, either directly or indirectly, if the polyp is part of a colony. The oral end bears the mouth, and is surrounded by a circlet of tentacles.