Don't know if you ever figured out what the snail was, but it's a marginellid, Prunum apicinum. They are predator/scavengers, and may kill and eat tiny animals in your tank, as well as scavenging bits of meaty leftovers. One or two won't be a problem, but a whole tank full might deplete your sandbed fauna.
http://www.gastropods.com/7/Shell_1957.shtml
Cheers,
Don
(PagoJoe)