No question in my mind. It is definitively a Eunice worm. There is only one rock in my tank that did not come from TBS, a zoa frag rock. I dipped that rock for 15 minutes in CoralRx, but I suppose it’s possible the worm survived the dip and moved into another rock.Are you sure that the worm had the appendages at the mouth that distinguish it from common bristleworms?
Typing this out, I’m betting that’s what happened. Because the Eunice worm I found does not appear to be native to the Gulf. At least, not based on any of the data I have found so far.