Lawnmower blenny. Their really cool, mine will come out when I get home and walk up to the tank. They follow you with their eyes, mine will follow my finger along the front of the glass. If I can't see mine, if I call its name (Nibbler) he'll come out, no kidding! He nibbles algae, cleans it off the glass, and since I dose with vinegar, he eats the bacterial films that form. Some people have trouble getting them to live long, I had in the past, but since vinegar dosing and watching them eat the film, I think that is the extra food source they need. The one I had before him was doing well, suddenly stopped eating and died, and upon reflection realized I hadn't been dosing vinegar on a regular basis. It also grazes on the live rock.