What do their shells look like? They were probebly on your plants..and are rams or pond snails. My tanks have both, the ponds and rams can bite up your plants as they get big...but They really don't mess it up as much as people said they would. They are usually eatting the algae that is on the glass wood rocks or plants. Rarely do I see a whole in the leaves.
I have a yoyo loach in the one tank to help control them. The trumpet snails wont eat your plants(spirial pointy shell),so that may be a good thing.