Sorry I'm so late to the game, but I love polychaete IDs and couldn't help myself. The large fatty in the center looks like it could be a member of hermodice carunculata, which are predatory of certain corals and give a very nasty "sting". I say that based on the appearance of the chaetae/setae i.e. Bristles. While the vast vast majority of "bristle worms" are beneficial, these nasties do sometimes find their way into tanks. I would be watchful at night and see if you find it preying on any sps or gorgonians.