Yep that's a dwarf lion. I've had him about 6-7 months. I've been careful about what I put in a tank with him. Nothing small enough for him to fit in his mouth has been kept in a tank with him. At one point I had another fuzzy dwarf with him, as well as a lawnmower blenny, and a bluespot jawfish. They were all in the 40 gallon cube, which was quite a bit bigger, and they all got along fine. The move didn't go well, and he's the only one from that tank that survived. I'm thinking of getting a small cowfish to put in there with him, but I'm not sure. Right now I can have hermits in the tank as the cleanup crew. I'm not sure that hermits would survive a cowfish. Starfish are out as cleaners because the harlequin will eat them. Snails probably wouldn't survive a cowfish either. I'll have to do some more reading before I decide what else I'll put in there.
I'm thinking one more non-reef safe critter.