Calcarea is a class of sponges (Porifera), not Cnidaria — and sponges do not have polyp stages at all. Among Cnidaria: Anthozoa (sea anemones, corals) exist only as polyps (no medusa stage); Hydrozoa and Scyphozoa have both polyp and medusa stages. Scyphozoa (jellyfish) are the 'true jellyfish' where the medusa is dominant. The question may contain an error in options; among Cnidaria, Anthozoa lack the medusa stage.