This time-lapse video was recorded during six hours at the Enoshima Aquarium in Fujisawa, Japan. It shows a Japanese spider crab shedding its shell. The crab measures over twelve feet across.
The first time I saw an image of that crab was in National Geographic. There was a diver stadning near it, to give you a idea of size. It was mostly leg. When you see one next to a diver - you then realize it aint that scary.
http://conservationreport.files.wordpress.com/2010/02/japanese-spider-crab.jpg