I have noticed a couple of small dime sized mojano in my tank. How harmful are they? Could they eat a goby. I ask because I cant figure out what happened to my mated pair of Twin Spots. One disappeared and then the other a couple days later. No remains (not surprising with my cleanup crew) and didnt jump out. I havent seen any signs of a mantis shrimp and inspected all my rock for any prior to placing it in the tank. The only other thing I have seen is a reddish looking worm centipede thing that I can only assume is a bristle worm. Dang I loved those gobies.