AP BIOLOGY

Detailed explanation-1: -Many species of the phylum Cnidaria have two separate life cycle stages: polyp and medusa. The phylum Cnidaria contains species that only exist in the polyp stage (Anthozoa), species that only exist in the medusa stage (Cnidaria), and species that occur in both life cycle stages (Cnidaria) (Hydrozoa).

Detailed explanation-2: -In the phylum Cnidaria, which includes jellyfish and sea anemones, polyp and medusa are two different stages of the life cycle. In some species, these two stages alternate between each other, such as in Hydrozoa.

Detailed explanation-3: -Cnidarians and Ctenophores. Hydrozoa are a class of jellyfish in the Phylum Cnidaria. Many of them show a phenomenon known as an alternating life cycle, which includes a benthic stalked (polyp) form, and free-swimming jellyfish (medusa) form.

Detailed explanation-4: -There are two basic cnidarian body shapes: a polyp form, which is attached to a surface; and an upside-down free-floating form called a medusa. Some cnidarians change form at different phases of their life cycle, while others remain in one form for their entire life.

Detailed explanation-5: -Some cnidarians go through both a polyp and medusa phase in their life cycle. However, one or the other is the dominant phase in different species. Figure 3.25 demonstrates some examples of body plans showing radial symmetry.