Hi Tristan,
These are cold-water snails from South Africa, and probably wouldn't do well in a reef tank. The snails you usually see pictured on the net have had part of the outer layers of shell polished away to reveal the pearly interior typical of the turbinids and trochids. When they are alive, the shells are usually encrusted and not all that beautiful.
Turbo (Sarmaticus) sarmaticus
There is another tropical species that is naturally pretty that you should be able to get for you reef tank. They don't get quite as large, with the typical size being two inches and a large one being three inches:
Turbo (Turbo) petholatus
Cheers,
Don