Barrel Jellyfish

In warm summers, large numbers of Barrel Jellyfish, harmless to humans, can be found in the seas round the Lizard.
Photo: Ray Surridge


Scientific name: Rhizostoma pulmo (synonym: Rhizostoma octopus)

Other common names: Dustbin-lid Jellyfish, Frilly-mouthed Jellyfish

Cornish name: morgowlesen is the general word for a jellyfish

What to look for:

  • Colouring and appearance: Varied in colour, including shades of pale yellow, green, blue and brown. The bell is dome-shaped and becomes more opaque when exposed to the air.
  • Size: Up to 90 cm in diameter, although it is more commonly about half this size
  • Where: Atlantic and Mediterranean


Find a Barrel Jellyfish washed up on the beach and you might be excused for being somewhat perturbed – these large marine creatures can reach up to almost a metre in diameter. In fact, they are harmless to humans. They have four pairs of tentacles (giving this jellyfish its previous scientific name of Rhizostoma octopus – ‘octopus’ of course means ‘eight-legged’). The tentacles are fused together for a large part of their length, and immediately below the bell form a cauliflower-shaped mass containing many very small stinging tentacles with which they trap plankton, feeding them into their digestive system via pores. These stinging cells are not anything like powerful enough to hurt humans (though you should always be cautious about touching jellyfish, especially if you are unsure of their identification).

Swarms of Barrel (and other) Jellyfish can occur in the warmer summer months, and can sometimes be found washed up on the beach. In the winter some may take refuge in deeper parts of the ocean.

Did you know…?

…A tasty meal: Leatherback Turtles love to eat Barrel Jellyfish. Leatherbacks visit UK waters in the summer.

…Hitching a ride: small crustaceans (Hyperia galba) cling on inside Barrel Jellyfish, avoiding predation by fish.




More information and references:

Turk, S.M., 1971. Seashore Life in Cornwall and the Isles of Scilly. D. Bradford Barton Ltd., Truro.

Published: May 2014
Author: Amanda Scott
Photos: Pictures of washed-up Barrel Jellyfish in Helford Estuary, 11 May 2014 – Ray Surridge; swimming Barrel Jellyfish – by Yoruno at it.wikipedia (Original text : Pino Bucca) [CC-BY-SA-3.0 (], from Wikimedia Commons