A lot of places mis label them ( some unintentionally, some intentionally) that may be what swf.com buys them as them as, but Ilyanassa obsoleta are not really great for a reef tank as they are from cooler waters originally, by being in our higher reef temps their metabolism is in constant overdrive, causing and extremely truncated life span. some places even list them as both nassarius and ilyanassa. but the nassarius snail we most commonly desire is Nassaurius vibex, not Ilyanassa obsoleta.
(this note is for the mods or maybe even admin, you may want to check into the species your ordering and recieving, as well as selling. Ilyanassa are far cheaper than nassarius you may be getting ripped off)