See text 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.

The three traditional families, Pelagiidae, Cyaneidae, and Ulmaridae, are distinguishable by these characteristics: In addition, members of the Pelagiidae have no ring canal, and the marginal tentacles arise from umbrella margin.

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