Flag Mouth Jellyfish (Semaeostomeae)


The Semaeostomeae (literally "flag mouths") are an order of large jellyfish in the class Scyphozoa found in coastal waters, particularly those of North America and Europe.

Five interesting facts about the flag mouth jellyfish:

  • It consists of five families: Cyaneidae, Drymonematidae, Pelagiidae, Phacellophoridae, and Ulmaridae.
  • It made up of more than 60 living species.
  • It includes the giant Cyanea arctica, which may attain 2 m in diameter.
  • The jellyfish have quadrate mouths with four lips and eight large tentacles at the margin of the umbrella.
  • Most species live in warm, coastal waters, a few in frigid waters; some oceanic.

Aurelia aurita
Moon jellyfish (Aurelia aurita), Scotland

Blue jellyfish
Blue jellyfish (Cyanea lamarckii), Scotland

Cyanea lamarckii
Blue jellyfish (Cyanea lamarckii), Scotland

Have you ever seen these jellyfish? Feel free to post a comment below.


  1. Oh they look fascinating! we had lots of Portuguese Man of Wars on our local beaches during the summer which were cool to look at but you had to keep the kids well clear!

  2. I could just stare at these all day because of the colours! I will be showing this post to my kids as they're obsessed with jellyfish.

  3. Interesante y bellas fotos. Saludos.