Wow. I may have to make a 12-gallon nanocube and a green mantis shrimp my first marine tank! Those are amazing and beautiful creatures.
So, what would be safe to place in a tank with a mantis shrimp? I know all fish, crabs, etc. are probably out (except as food!), but what about snails? urchins? corals? Can anything else live with one of these little terrors?