Discomedusae

thumb|right|"Discomedusae" (all rhizostomids), 88th print of Ernst Haeckel's [[Kunstformen der Natur, 1904]] Discomedusae is a subclass of jellyfish in the class Scyphozoa. It is the sister taxon of Coronamedusae. Discomedusae contains about 155 named species and there are likely to be many more as yet undescribed. Jellyfish in this subclass are much more likely to have swarming events or form blooms than those in Coronamedusae. Discomedusae consists of two orders, Rhizostomeae and Semaeostomeae.

==Rhizostomeae== Members of the order Rhizostomeae are collectively known as "root-mouth jellies" and are very diverse. They do not have tentacles or other structures at the edge of the bell, instead they have eight oral arms which fuse together to form the manubrium, a central organ with the mouth at its tip, resembling an elephant's trunk. Some have numerous manubrial outgrowths, well-armed with cnidocytes and mucus-secreting cells; others have the central manubrial mouth closed, instead making use of secondary mouths at the side of the manubrium. These adaptations give the jellyfish a large surface area with which to collect large quantities of planktonic organisms. It can trap plankton from the water currents it produces by pulsating.