How important are snails?

[Enigma]

I don't have any of the Big guys you've got . . . I forget what they're called right now. I think six might be overkill. I'm not sure what they eat.

I have Mexican Turbos, Spiny Astrea, Nassarius, and Ceriths. They're all very useful to me, and I need more.

I figure that if what you've got isn't doing the job you want them to do, it is probably time to pass them on to someone else or return them to the store. If they're the big guys I'm thinking of, I skeptical that they'd be appropriate for your sump.


Edit: are cowries what you've got?