The monstrous specimen, which weighed 9.25lbs with a 1ft wide shell and 2ft wide claw span, shocked fishmonger Simon Finch when it was delivered to him on Wednesday.
The average brown crab weighs between 1 and 2lbs - but there must have been something in the water where the beastly crustacean lurked, 25 miles off the coast of Littlehampton, because the smallest of the six-crab haul was 7.5lbs.
Even this tiddler beat the weight of the previous largest crab Mr Finch had seen in his 20-year career last year. Click here to read more.He said: "They were colossal. This really is an exceptional find.
"They are so big, they could literally snap your arms if they got hold of it. There is so much power in those claws. They could break your bones."
The 45-year-old from Littlehampton said from the size of the largest crab, it must be between 50 and 70 years old. He said it was 'miraculous' the behemoth lived to that age, given the amount of fishing in the area and that for a few weeks of the year, the crabs shed their shells and are vulnerable to predators.
He said: "They are like jelly; you could screw them up like a wet paper bag."
When they shed their shells to grow larger, the crustaceans have to force their claws through a small hole, and often they will drop off through stress as a survival mechanism. In this case, Mr Finch said the largest crab's claws were so big they must have been the original pair.
The biggest specimen sold for £40 at his shop, Riverside Fish in Arun Parade Littlehampton.
Mr Finch said: "They really surprised customers - all week people were taking photos with them, and the kids loved it.
"People think when they go crabbing that is how big they get, but these are remarkable."
And it isn't just crabs. The fishmonger got a surprise when five nine-pound lobsters were found off the coast.