Nope. It's a Polychaete in the Amphinomid family. Harmless/ beneficial detrivore. It will eat any food the fish miss as well as their waste. The perfect reef janitor.
Great so its not a Bristle worm when I did a search it looked like one but all the info that I could pull up say they move fast. :lol: will they breed in the tank?
Well, yes it is a Bristle Worm. It will multiply in direct proportion to the available food in the tank. If there's a lot of food they will quickly multiply.