Small spiral/conical shape or mini-turbo looking? If the first, they are probably pyramid snails and they come in two forms, those that prey on clams and those that prey on Asterina snails. There are probably many types, but those are the common ones.
Manual removal of the snails themselves, the hosts. Put them into a bucket of water from the tank and light scrub them off with a toothbrush. You brush to rid the eggs too which look like snot, a clear viscous slimy substance. The snail predators are harder to rid yourself of than the clam variety since its hard to remove and scrub every snail.
