The class of the Scyphozoans owes its name to the Greek word 'skyphos' which means bowl or cup. These are Cnidarians among which we will find the largest species, such as the Arctic lion's mane jellyfish (Cyanea capillata) whose diameter reaches 2 meters and with tentacles that can reach up to 60-70 meters in length and 220 kilos in weight, or the case of Rhizostoma luteum that can reach up to 40kg in weight. Generally, and with the exception of the above cases, the size of the Scyphozoans usually ranges from 2 to 40 cm in diameter.

During their life cycle, Scyphozoans alternate between the polyp and jellyfish phases, although the polyp phase is usually very short, hence they are colloquially known as jellyfish.

One of the distinguishing features of this class is the absence of a veil at the end of the umbrella (body of the animal). In the Scyphozoans, the sexes are separated, with female and male specimens. Fertilization is internal, transporting the sperm by currents generated by cilia, to the female's gastric cavity where fertilization occurs.

There are approximately 200 species described, all of them marine.