Semaeostomeae

(invertebrate zoology) An order of the class Scyphozoa including most of the common medusae, characterized by a flat, domelike umbrella whose margin is divided into many lappets.

An order of the class Scyphozoa including most of the common medusae. The umbrella of these medusae is more flat than high and is usually domelike. The margin of the umbrella is divided into many lappets. Sensory organs are situated between the lappets. The tentacles are generally well developed and very long except in a few forms.

The life history of this group shows the typical alternation of generations, with forms passing through several larval stages. The Semaeostomeae are distributed mostly in temperate zones and are generally coastal forms with a few exceptions. Some of them are known to have violent poison on their tentacles. Several fossils of this group were found in the strata of the Jurassic period. See also Scyphozoa.

Semaeostomeae
Scientific classification
Kingdom:	Animalia
Phylum:	Cnidaria
Class:	Scyphozoa
Order:	Semaeostomeae L. Agassiz, 1862
Families
See text.

Semaeostomeae (literally "flag mouth") is an order of large jellyfish characterized by four long, frilly oral arms flanking its quadrate "mouth." Its gastrovascular system consists of unbranched pouches and it has no ring canal. Five families have been described.

Families

• Cyaneidae
• Depastridae
• Halicyathidae
• Pelagiidae
• Ulmaridae

Gallery

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

References

• Ruppert, Edward E.; and Fox, Richard S. (1988). Seashore Animals of the Southeast, University of South Carolina Press, 273. ISBN 0-87249-535-3.
• Hayward, Peter J.; and Ryland, John S. (1995). Handbook of the Marine Fauna of North-West Europe, Oxford University Press, 65. ISBN 0-19-854055-8.

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