EVERYDAY SCIENCE

Detailed explanation-1: -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-2: -Some examples of hydrozoans are the freshwater jelly (Craspedacusta sowerbyi), freshwater polyps (Hydra), Obelia, Portuguese man o’ war (Physalia physalis), chondrophores (Porpitidae), “air fern” (Sertularia argentea), and pink-hearted hydroids (Tubularia).

Detailed explanation-3: -Hydra never goes through a medusoid stage and spends its entire life as a polyp. However, Hydra is not typical of the Hydrozoa as a whole. Most hydrozoans alternate between a polyp and a medusa stage-they spend part of their lives as “jellyfish” which are hard to distinguish from scyphozoan jellyfish.

Detailed explanation-4: -physalis is a free-floating hydrozoan colony; each specimen is made up of many hundreds of organisms, each specialized for a certain function, including motility and buoyancy, feeding, reproduction and defense.