It's definitely a harmless Nassarius, although I'm not 100% certain which species. Neither conchs nor Nassarius absolutely require a sandbed, although most nassarius species do burrow in the sand. Several conch species actually live in coral rubble areas with no sand, but the smaller species normally seen in the aquarium trade usually prefer muddy sand areas (Conomurex luhuanus, the "Tiger Conch" of aquarium suppliers), or clean sand with some vegetation (Florida Fighting Conch, Humpback Conch, and others).