A 3.5ft (1m) long fish-eating bobbit worm has been found in a tank at an aquatics store in Surrey.
The sea creature was found at the Maidenhead Aquatics branch in Woking when a 200 gallon tank was emptied on Wednesday last week.
The worm, which has jaws twice the width of its body, was found in the last bit of rock in the tank.
John Penny, the store's manager, said the find had come as a "big surprise" to staff.
He said the store would keep the worm, which is living in a tank on the counter.
"When we took it out of the tank, it split into three sections," he said.
"One died and the middle section has started reacting to shrimps and moving around the tank."
Sliced in half
He said the worm had also spun a mucous web around itself.
The worm, which lives on the sea floor, is thought to have entered the aquarium in imported rock.
"Some little creatures can survive in live rock in transport. On occasion you get these worms but they're not that common, especially not at this size," Mr Penny said.
The creature is thought to have survived on food that was being fed to the fish in the tank.
Armed with sharp teeth, it is known to attack with such speeds that its prey is sometimes sliced in half.