Cnidarians
Cnidarians are a phylum composed of animals that live in an aquatic environment. They can present the form of a polyp or jellyfish during their life cycle.
Polyps are structures that are attached to the substrate, therefore, they are fixed structures, like sea anemones and corals.
Therefore, considering the options that the exercise presents, we can say that the only cnidarians that are just polyps are "Sea Anemones" and "Corals".