If it's a whelk, I don't recognize the species. It seems to have that "distorted" look, like a juvenile columbellid or strombid. Since I don't know any strombids with that color pattern, I'm going to guess it's a dove shell, which should do fine in your tank. It could also be one of the smaller species of Nassarius, I suppose, but even a juvenile would normally not be that skinny at the anterior tip/siphonal canal. Let us know if it looks like it's eating anything it shouldn't.
Cheers,
Don