Barrel jellyfish, the size of dustbin lids, have been spotted in large numbers on the Cornish coast.
The species has a thick rubbery dome the size of a dustbin lid, with cauliflower-like tentacles hanging down nearly two metres deep.
It's thought their food - plankton - is in bloom close to shore.
The barrel jellyfish is the biggest found in British waters.
Although they are not dangerous to humans, people are being advised not to touch them.
Watch Martin's report to find out more.