[pogodzib]

Are you sure that you're seeing small crabs and not the clams gills? If it is a pair of crabs, I'd contact the person that you purchased the clam from to inform them that your clams has crabs inside of it and if it dies that you want a replacement at no cost. There are plenty of crabs that will pick away at and eat crabs, but I don't know of any that are beneficial to crocea clams.