Semaeostomeae
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Semaeostomeae (literally "flag mouths") is an order of large
jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...
characterized by four long, frilly
oral arm An oral arm is an anatomical structure of "true" sea jellies (or Scyphozoans), which belong to the class Scyphozoa. Oral arms characterize Semaeostomeae, an order of large jellyfish. The oral arms (of which there are usually four) are located ...
s 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.


Taxonomy

The order consists of five families. * Family
Cyaneidae The Cyaneidae are a family of true jellyfish. About 20 species are in this family, including the well-known lion's mane jellyfish, lion's-mane jellyfish. Species The following species are recognized within the family Cyaneidae. Formerly, this f ...
* Family
Drymonematidae ''Drymonema'' is a genus of true jellyfish, placed in its own family, the Drymonematidae. There are three species: '' Drymonema dalmatinum'', '' Drymonema gorgo'', and '' Drymonema larsoni'', which are found in the Gulf of Mexico, Atlantic Ocean ...
Bayha, K. M., and M. N. Dawson (2010). ''New family of allomorphic jellyfishes, Drymonematidae (Scyphozoa, Discomedusae), emphasizes evolution in the functional morphology and trophic ecology of gelatinous zooplankton.''
The Biological Bulletin ''The Biological Bulletin'' is a peer review, peer-reviewed scientific journal covering the field of biology. The journal was established in 1897 as the ''Zoological Bulletin'' by Charles Otis Whitman and William Morton Wheeler. In 1899 the title ...
219(3): 249–267
* Family
Pelagiidae The Pelagiidae are a family of jellyfish. Members of the family ''Pelagiidae'' have no ring canal, and the marginal tentacles arise from umbrella margin. Genera There are four genera currently recognized: *Genus '' Chrysaora'' – (14 species) ...
* Family
Phacellophoridae ''Phacellophora'', commonly known as the fried egg jellyfish or egg-yolk jellyfish, is a very large jellyfish in the monotypic family Phacellophoridae containing a single species ''Phacellophora camtschatica''. This genus can be easily identified ...
* Family Ulmaridae


Differentiation

The three traditional families,
Pelagiidae The Pelagiidae are a family of jellyfish. Members of the family ''Pelagiidae'' have no ring canal, and the marginal tentacles arise from umbrella margin. Genera There are four genera currently recognized: *Genus '' Chrysaora'' – (14 species) ...
,
Cyaneidae The Cyaneidae are a family of true jellyfish. About 20 species are in this family, including the well-known lion's mane jellyfish, lion's-mane jellyfish. Species The following species are recognized within the family Cyaneidae. Formerly, this f ...
, and Ulmaridae, are distinguishable by these characteristics: *
Gastrovascular cavity The gastrovascular cavity is the primary organ of digestion and circulation in two major animal phyla: the Coelenterates or cnidarians (including jellyfish and corals) and Platyhelminthes (flatworms). The cavity may be extensively branched into ...
divided by radial septa into rhopalar and tentacular pouches **Pouches simple and unbranched – Pelagiidae **Pouches branched – Cyaneidae *Gastrovascular system in form of unbranched and branching canals, or with anastomosing radial canals – Ulmaridae In addition, members of the Pelagiidae have no ring canal, and the marginal tentacles arise from umbrella margin. Three genera are in this family.


Gallery

Image:Haeckel Discomedusae 18.jpg Image:Haeckel Discomedusae 28.jpg Image:Haeckel Discomedusae 8.jpg, "Discomedusae" plate from
Ernst Haeckel Ernst Heinrich Philipp August Haeckel (; ; 16 February 1834 – 9 August 1919) was a German zoologist, natural history, naturalist, eugenics, eugenicist, Philosophy, philosopher, physician, professor, marine biology, marine biologist and artist ...
's ''
Kunstformen der Natur (known in English as ''Art Forms in Nature'') is a book of lithographic and halftone prints by German biologist Ernst Haeckel. Publication Originally published in sets of ten between 1899 and 1904 and collectively in two volumes in 1904, it c ...
'', 1904


References

*Collins, A. G.; Jarms, G.; Morandini, A. C. (2022). "Semaeostomeae"
''World Register of Marine Species''
Retrieved 1 November 2022. *Ruppert, Edward E.; and Fox, Richard S. (1988). ''Seashore Animals of the Southeast'', University of South Carolina Press, 273. . *Hayward, Peter J.; and Ryland, John S. (1995). ''Handbook of the Marine Fauna of North-West Europe'', Oxford University Press, 65. . *Bayha K., Dawson M. (2010) New family of allomorphic jellyfishes, Drymonematidae (Scyphozoa, Discomedusae), emphasizes evolution in the functional morphology and trophic ecology of gelatinous zooplankton. Biological Bulletin 219: 249–267. Discomedusae Cnidarian orders {{Scyphozoa-stub