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It very well could be a carnivorous snail. There are plenty that aren't reef safe and some that are downright deadly to humans. Observe it's behavior, if you or someone can't ID It and determine whether to remove them.
No refugium, but I have a qt tank that I could pop it in. I probably would have done that if I could have gotten to it quick enough. After I snapped the picture, it disappeared. I'll search for it again when I get home.