Oy. Polychaete means "many bristles" and includes thousands of species including those pretty feather dusters people spend twenty to forty bucks on. Of the thousands of species of polychaete worms, there are a small handful that are potentially harmful. That's neither a Caribbean bearded nor a bobbit worm, and other than those two, the potentially harmful typed almost never get into our tanks. It's your average every day run of the mill bristle worm. It is very unlikely to ever exceed a few inches long and doesn't have the mouthparts necessary to eat corals. It is a scavenger, and a highly efficient one at that. These worms are villainized because they are worms.