Which class of the phylum Cnidaria is exclusively in the medusa form?

The Class Scyphozoa, often referred to as the "true jellyfish," predominantly exhibits the medusa form throughout its life cycle. In this class, the medusa is the dominant and recognizable stage, characterized by a bell-shaped body and tentacles that can be long and trailing. Scyphozoans are known for their gelatinous structure and, while they may have a polyp stage early in their development, this stage is not as prevalent or recognized as the medusa stage.

In contrast, members of the Hydrozoa class can exhibit both polyp and medusa forms, with some species being primarily polyp-centric. Anthozoa, which includes corals and sea anemones, only exists in the polyp form and does not have a medusa stage at all, making it clear that they are not exclusive to the medusa form. Hence, Scyphozoa is established as the only class within Cnidaria where the medusa is the primary life stage and is extensively recognized for its adult form.