Shelless Snail?

[Delphinus]

Stomatella varia are harmless algae eaters who will reproduce in your tank. A total benefit to a tank IMO.

http://www.reefs.org/hhfaq/pages/pic...tomatella.html

Only thing is they're fairly delicate and defenseless and will get munched/predated. You have to be very gentle with them - they'll also get ripped in half if you try to pick them up too roughly. So they tend to come out more at night when it's safe ("safer" might be the better term). When I had cleaner srhimps, they pretty much stripped the display tank of all Stomatella in there. Stupid shrimp.