Barrel jellyfish

Thousands of Giant Jellyfish in Britain Coast (8 year old article)

More pics in article link

Original text from french:

In the waters off the English coast, huge jellyfish have been found and captured by photographer Steve Trewhella who works for the Daily Mail. Jellyfish "Rhizostoma pulmo" are known for their giant size but also for being harmless; the photographer was therefore able to swim alongside them.