So I have these things all over my sump! They are not in the display, leading me to think they might be tasty, or light averse. They are sedentary, or at least always in the same locations. It definitely came in on a coral frag. I know which one in fact. I thought at first they might be a tunicate, but I don't think so now. It's not a great photo (I am perhaps the world's worst photographer!), but perhaps someone has suggestions. Thanks in advance for any ideas!