Here is a COMPLETE article on snails and no you don't need to feed them...They eat most the left over junk and algae that is in your tank. And I think the snails you have are Cerith. The come up like little submarines, Turbo's do not bury they stay on the rock and the glass, mostly.
Anyone, correct me if I'm wrong.....
The Clean Up Crew
Are they Tang?? Hmmm