Crab legs can and sometimes do have parasites on them.
The crab can pick up parasites on it's legs as it walks across the beach or swims around in the ocean and those parasites can transfer from the beach and the ocean and get onto the crabs legs.
However when you cook the crab fully or cook the crab legs fully then those parasites should be killed and not live so if the crab legs you cooked or the crab you cooked contained any parasites then you should not get infected with those parasites yourself.
Cooking the crab to a high enough temperature kills off any parasites but a crab or crab legs that are not fully cooked may still contain parasites.
Yes you can eat the dead man on the crab although the dead man part of the crab is not very tasty.
The dead man part of the crab is not toxic or harmful nor is the dead man on the crab poisonous as some people have been told or believe.
The dead man of the crab is edible but it's not very delicious to eat so you would probably not like it but some people do.
I tried the dead man part of the crab before and hated it but it's edible.
The dead mans fingers of the crab are essentially the gills of the crab that are elongated, spongy-looking organs that enable the crab to be able to filter air from the water and help it breathe.
The dead mans fingers on the crab are not poisonous and will not kill you if you eat them.