Which group of animals has two variations in their basic body plan, a medusa form and a polyp form?
Coelenterates have two body forms polyp and medusa.
Hydrozoa scyphozoa and anthology are the three classes of coelenterates. Hydrozoans have polyp form predominant. It means most of the life exists in polyp former.
Scyphozoa are jellyfish like animals have medusa form for most of the time. Their polyp stage is only larval form.
Anthozoa are searching anemones and corals. They have polyp stage for most of the time.
Polyp and medusa are alternation of generation.