snails ate one of my emerald crabs...sucked him straight out his shell. tried like 100 times to keep them a part.
but i was too late in taking it out the tank.
If they are on your leather, just pluck them off with a tweezers and get rid of them. It may take a number of times before you get them all. I battled predacious nudibranches on a Colt like this... took a while, but worked.