The man-of-war has stinging tentacles which can grow up to 165ft (50m)
A live Portuguese man-of-war jellyfish has been found on the Dorset coast.
Monday's find in Kimmeridge Bay is the third to be reported in the past few days in the county, even though the jellyfish is rarely seen in UK seas.
Dorset Wildlife Trust said others had been spotted at Burton Bradstock and Durdle Door.
It urged the public to report any further sightings of the potentially dangerous jellyfish, but not to touch the creatures.
The man-of-war usually lives in tropical waters and the trust has put the appearances down to recent strong winds.
The long tentacles of a man-of-war, which hang from a balloon-like float resting on the surface, can produce an extremely painful and potentially dangerous sting.
Julie Hatcher, Dorset Wildlife Trust marine warden, said: "We haven't seen any of these in Dorset for several years and you wouldn't want to meet one while swimming.
"They are very rare here, but every few years we see some blown across the ocean.
"There could still be more about, so we would advise people not to touch them but to let us know."
A man-of-war was also found last week in Smuggler's Cove, near Holcombe, Devon.
Man-of-war colonies are usually found in places such as the Florida Keys and Atlantic coast, the Gulf Stream, the Gulf of Mexico, the Indian Ocean and the Caribbean.
The 6in (15cm) specimen found on Monday can be seen in the Marine Centre in Kimmeridge Bay.