Those are Caribbean star polyps sometimes you can get royal damsels to eat them but a i got ride of mine by starving them. I ran so much carbon replacing it every week which i believe took so many nitrients out of the water they starved to death. There are officially no more in my system. However i lost many other zoas and cloves and star polyps as well. So if you dont want that to happen you can control them by sucks them out and using aptasia x to keep them at bay.