The class of coelenterata in which the medusa and polyp both are found in one animal is

The correct option is Hydrozoa.

Coelenterates (or Cnidarians) are characterized by having two primary body forms in their life cycles:
1. Polyp: A sessile (stationary), asexual, and cylindrical form (e.g., Hydra).
2. Medusa: A free-swimming, sexual, and umbrella-shaped form (e.g., jellyfish).

Let us analyze the classes of Coelenterata to understand where both forms coexist in a single organism's life cycle:

• Hydrozoa: In this class, alternation of generations (metagenesis) is highly prominent. Organisms typically exhibit both polyp and medusa stages during their life history. For instance, in Obelia, the polypoid colony reproduces asexually to form medusae, which then reproduce sexually to produce larvae that grow into polyps. Thus, both forms are represented in the life cycle of a single animal species.

• Scyphozoa: In this class (true jellyfish), the medusa stage is dominant and large, while the polyp stage is either reduced to a tiny, brief larval phase (scyphistoma) or completely absent.

• Anthozoa: Members of this class (like sea anemones and corals) exist exclusively as polyps. The medusa stage is entirely absent in their life cycle.

Therefore, the class of coelenterata in which both the medusa and polyp stages are found in one animal's life cycle is Hydrozoa.