An experienced diver told how he "wrestled" a 3ft (0.9m) lobster into a string bag after it attacked him.
Lemmy is estimated to be about 50-years-old
Chris Hovard, from Wyke Regis, Dorset, was diving when the creature - weighing more than 10lbs - scuttled towards him near Weymouth jetty on Saturday.
The 51-year-old, who has been diving for 34 years, said he had never seen a crustacean "anywhere near this size".
The lobster, which he named Lemmy after the lead singer of rock band Motorhead, is now at Weymouth's Sea Life Park.
Mr Hovard said: "I was diving when I spotted an old boiler which I believe may have been used in the Northe Fort in the olden days and then was thrown into the sea when it was no longer needed.
"I was swimming around it when the lobster came at me, its claws snapping.
"I could hardly get my hand across the back of its shell.
"You'd need a saddle to ride it. I managed to get it with a pincer movement.
"The commotion stirred up a silt cloud which momentarily stunned him and this was when I managed to grab him."
The Northe Fort is a restored Victorian fort now used as a museum.