Medusa (biology)
In the class Hydrozoa, medusae are the sexual individuals of many species, alternating in the life cycle with asexual polyps. The medusa form of Hydrozoans are known as hydromedusae. A polyp is the form that attaches to a surface, while a medusa is the form that is free-floating; a species of cnidarian may take each form in a different phase of its life.