dead snail shells with holes

[draco]

Looking in our tank we noticed our snails died ,we had just bought them 2 weeks ago, seemed it a little strange they were all in a pile had a close look there is holes in the shells. what could have done this .please help it is right by a rock . Two clowns ,citrus goby,2 twin spot (signal) goby,yellow headed jawfish ,fire fish,2 cleaner shrimp,1 fire shrimp, hermit crabs.