We just did a 3 day blackout to try and kill off some Dinos and when we opened it back up this was on one of our rocks it was just a tube at first but has since opened up my first thought it was an Aiptasia but it looks different from those that I have killed maybe because the blackout, the tube is long and has just short tenacles and there is a fluorescent green dot right in the middle the stem is about 1/4 diameter and bout 1 inch long