Velella velella are only thought to live for about a month
Thousands of jellyfish-like creatures have been found on beaches in Cornwall.
The 10cm (4in) long, bright blue by-the-wind-sailors, or velella velella, were found near Penzance and identified by Newquay's Blue Reef Aquarium.
The stranding is thought to coincide with the warming of coastal waters, the aquarium said.
The animals are not a threat to humans or pets, but people who have handled them should avoid touching their own faces, Cornwall Wildlife Trust said.
Staff at Cornwall Council's beach and pools department contacted the aquarium to help identify the creatures after large numbers were found washed ashore.
Velella velella live in warm and temperate waters in all the world's oceans and are relatives of the Portuguese Man-o-War. However, they are not classed as jellyfish.
David Waines, from the aquarium, said: "By-the-wind sailors travel the world's oceans in huge flotillas sometimes made up of hundreds of thousands and even millions of individuals."
He said if prevailing winds changed direction they could wash up on beaches in great numbers.
"They are predators and use their dangling tentacles to catch small invertebrates and fish.
"They do have a small sting to capture their prey but most humans would feel only a tingle if they had sensitive skin."
They are only thought to live for about a month.