Sue Daly / Barrel jellyfish (Rhizostoma octopus) swimming past, Sark, British Channel Islands, UK, September.

Stephane Granzotto / Jellyfish (Rhizostoma pulmo) Mediterranean sea, Corsica

Stephane Granzotto / Jellyfish (Rhizostoma pulmo) Mediterranean sea, Corsica

Stephane Granzotto / Jellyfish (Rhizostoma pulmo) Mediterranean sea, Corsica

Stephane Granzotto / Jellyfish (Rhizostoma pulmo) Mediterranean sea, Corsica

Stephane Granzotto / Jellyfish (Rhizostoma pulmo) Mediterranean sea, Corsica

Graham Eaton / Rhisostome / Barrel jellyfish (Rhizostoma octopus) stranded on a sandy beach, Abersoch, Gwynedd, Cardigan Bay, Wales, April.

Sue Daly / Barrel Jellyfish (Rhizostoma pulmo) against crepuscular light rays. Sark, British Channel Islands, July.

Sue Daly / Barrel Jellyfish (Rhizostoma pulmo) against crepuscular light rays. Sark, British Channel Islands, July.

Sue Daly / Barrel Jellyfish (Rhizostoma pulmo) Sark, British Channel Islands, July.

Philippe Clement / Barrel jellyfish (Rhizostoma octopus) washed up on beach along the North Sea coast, Nord-Pas-de-Calais, France, August

Jeff Rotman / Barrel jellyfish {Rhizostoma octopus} indicating plankton migration, Irish sea.

Jeff Rotman / Barrel jellyfish {Rhizostoma octopus} indicates plankton migration, Irish Sea, UK

Bernard Castelein / Barrel jellyfish stranded on beach {Rhizostoma octopus} Texel, The Netherlands

Sue Daly / Barrel jellyfish {Rhizostoma octopus} Jersey, Channel Isles, UK

Philippe Clement / Barrel jellyfish (Rhizostoma pulmo) washed ashore on the beach along the North Sea coast in summer, Belgium. September.

Philippe Clement / Barrel jellyfish (Rhizostoma pulmo) washed ashore on the beach along the North Sea coast in summer, Belgium. September.

Guy Edwardes / Stranded Barrel jellyfish (Rhizostoma pulmo) on beach, Whiteford Sands, Gower Peninsula, Wales, UK. August.

Nick Upton / Barrel or Dustbin-lid jellyfish (Rhizostoma pulmo) stranded on a sandy shore, The Gower, Wales, UK, September.

Nick Upton / Barrel or Dustbin-lid jellyfish (Rhizostoma pulmo) stranded on a sandy shore, The Gower, Wales, UK, September.

Chris Mattison / Barrel jellyfish (Rhizostoma pulmo) washed up onto West Angle beach, South Pembrokeshire, Wales, UK.

Philippe Clement / Barrel jellyfish / Dustbin-lid jellyfish (Rhizostoma pulmo) washed ashore on the beach along the North Sea coast in summer, Belgium, July