I have a Bristle Worm in my SW tank. Should I take it Out?

It's fairly large... probably about 5 or maybe even 6 inches long. Gray and white in color. I have had my tank up and running and fully established for probably about 3 or 4 weeks now and JUST noticed it today! I have 2 balloon mollies and 1 hawaiian reef hermit crab and it hasn't bothered anything. I am only doing a FOWLR tank so do I need to take it out if I'm not going to have any corrals or invertebrates? I hear that I should because of it's size.