The Scyphozoa is currently divided into the following four orders:
Order Stauromedusae These are sessile cup-shaped forms, and lack a
Order Coronatae Most of these are deep-dwelling jellyfish, and are thus
Order Semaeostomae The so-called disc jellyfish, including the most
common as well as the largest of the jellyfish.
Order Rhizostomae These jellyfish lack tentacles, and have eight oral
arms instead of four. The oral arms, often highly branched, have become fused in the center,
closing off the central mouth and giving the jellyfish multiple mouth openings
at the ends of the lateral arms.
The Cubozoa, or
box jellies, were at one time included as an order of the Scyphozoa, but
are now considered to be the sister group of the jellyfish.