Barrel Jellyfish

Barrel jellyfish

Latin name: Rhizostoma pulmo
Global Distribution: NE Atlantic, Adriatic, Mediterranean Sea, Black Sea, Sea of Azov
UK Distribution: South and West Coast
Size: 40cm (occasionally up to 90cm)
Diet: Plankton
Habitat: Pelagic

The Barrel Jellyfish, also known as the dustbin-lid jellyfish or the frilly-mouthed jellyfish, is an impressive creature with a huge dome jelly up to 90cm wide and cauliflower like fused tentacles dangling up to 1.9m below. The stings are harmless to humans. A blue line runs round the edge of the dome with tiny dots evenly spaced. These sensory statocysts help them work out their orientation in the water. The scientific name Rhizostoma means ‘root pores’. The cauliflower like fused tentacles hang down below the solid dome. Hundreds of small mouths (the pores) are surrounded by tiny stinging tentacles that collect plankton and take it to a highly branched digestive system.

The barrel jellyfish plays host to amphipods (Hyperia galba), crustaceans up to 1cm long, that hang onto the jelly with spine-like feet, often inside the stomach or reproductive cavities. These can change colour to match the jellyfish tissue to avoid being eaten by fish.  If an over infestation occurs they can kill the jellyfish. Experts believe the growing numbers of Jellyfish in British seas could be a result of pollution, over-fishing or climate change. Jellyfish are the staple diet of the critically endangered leatherback turtle and the small jellyfish polyps are eaten by fish.

Fun facts

  • Despite their stings not being harmful to humans these jellyfish still caused a media sensation where swarms of them were washed up on UK beaches in May 2017.