Yes it definitely looks like a bristle worm. Bristle worms are not necessarily bad, but nor are the necessarily good! I found that if kept in "check" they can be an asset as part of the CUC. BUT if allowed to get out of hand, they can be a MAJOR problem and they can become easily out of hand! Over feeding is usually the result that allows them to become "over populated". When over populated I've seen them attack clams, corals and other inverts.