Scyphozoa

The Scyphozoa are an exclusively marine class of the phylum Cnidaria, sometimes referred to as the "true jellyfish" (or sea jellies - as they are not, in fact, fish).

The class name Scyphozoa comes from the Greek word skyphos (σκύφος), denoting a kind of drinking cup and alluding to the cup shape of the organism.

Scyphozoans have existed, in geological time, from the Ediacaran period to the present.

Biology

Most species of Scyphozoa have two life history phases, including the planktonic medusa or jellyfish form, which is most evident in the warm summer months, and an inconspicuous, but longer-lived, bottom-dwelling polyp, which seasonally gives rise to new medusae. Most of the large, often colorful, and conspicuous jellyfish found in coastal waters throughout the world are Scyphozoa. They typically range from 2 to 40 cm (0.79 to 15.75 in) in diameter, but the largest species, Cyanea capillata can reach 2 metres (6.6 ft) across. Scyphomedusae are found throughout the world's oceans, from the surface to great depths; no Scyphozoa occur in freshwater (or on land).