Hi, I wondered if anyone could tell me what this is. At first my brother has scared me by telling me it was a Majano but I didn't think it looked like one and when I posted these pics in another forum most thought it was some kind of mushroom. It just sort of showed up in my tank about 6 months ago and I just left it alone. It has gotten much larger (when opened up it is probably 3" across) and now there are 3 little ones on the live rock next to it. When the tank lights are off it shrinks down to about 1/2 the size it is when the lights are one and it opens up. Any thoughts on what it is and if it is bad to have in a small tank?