Yup, bristle worms, I have a bunch in my tank. At night, they go to town and eat all the detritus in the water. So, I let them be. Just DO NOT touch them, those lil bristles are their defense mechanism, it will burn you, and if you are allergic you might need a shot. My suggestion is, wear gloves, Nitrile are best because they are puncture proof. Or get the aquagloves.