Semaeostomeae

Semaeostomeae
Sea nettles, Chrysaora fuscescens
Scientific classification
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Scyphozoa
Order:	Semaeostomeae L. Agassiz, 1862
Families
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The Semaeostomeae (literally "flag mouths") are 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 order consists of five families.

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. Three genera are in this family.

"Discomedusae" plate from Ernst Haeckel's Kunstformen der Natur, 1904

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