You also have to worry about the eggs the pyramid snails lay. They look like a small clear slimy mass. They could be up by the mantle or down by the byssus gland. Put the clam in some saltwater from the tank and use a stiff tooth brush and scrub it down good taking care not to scrub any mantle showing or the byssus gland. That should get rid of snails, eggs or sponges. Look carefully. Rinse in fresh saltwater and then place in qt for a few weeks to be sure you didn't miss anything.