It actually eats algae, which makes me wonder if it's a true money cowrie. I've seen it crawling across the glass leaving a trail of algae-free glass behind it. I don't intentionally feed it, though I'd offer it food if I could find it during feeding time.
I'm sure it's out and around, I probably just can't see it. It looks like a lump, and I usually only notice it when it's on the glass.