They call this crab/dish KAGANG (which I think was derived from the local dialect kagang-kagang for palm grass which seems to be the one used in the dish). Basically some of the crabs are opened and flaked, the meat mixed with coconut meat and spices, and stuffed back into the crab shells. Some of the mixture is also mixed with sticky rice (I think) and wrapped in the palm grass, which is then tied to a crab. All this is cooked in a big pot of coconut cream.
This is a delicacy in Marinduque that travellers should make sure to sample. Just ask the locals where you can order some.