does it live below the sand line? looks like it does. If not a Nassarius species, then my next guess would be a conch type, like an oyster drill. It depends on the shape of the opening. If it's round, it could be a cerith, but if not, then a conch type. Does it look like it's eating algae? then its a cerith. If not, and it looks like there is a tube/probe sticking out the front, then is a conch type predator.