I've got what I took me a while to identify as a eunicid rock worm in my 4 gal pico. He's about 4 inches long (at least the part of him that comes out) so far he hasn't bothered anything and lives in my zoa rock but he's pretty big and at this point I have to dangle a piece of silver side in front of his cave and feed him or he jacks everyone else's food.