I'm hoping the photo is good enough for an ID. I think it's a stomatella but I'm quite far from being an expert. It did have a partial shell on top. But I've never seen a live one, or a dead one, so I would like someone with a little more experience to make the call.
Yup, I think you are right... I have a bunch in my 150, and now also in the 180... Stomatella snails are beneficial for reef aquariums as they are herbivores that will help control micro algae growth.