Discomedusae

Semaeostomeae (literally "flag mouths") is an order of large jellyfish characterized by four long, frilly oral arms flanking their quadrate mouths. The umbrella is domed with scalloped margins, and the gastrovascular system consists of four unbranched pouches radiating outwards from the central stomach; no ring canal is present. They usually possess eight tentacles; four are per-radical and four are inter-radical.

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.