Slow down and don't kill it!!! It looks like a bubble corallimorpharian. I have 3 in my tank and the largest one is about 6" across. It does not look like a mojano anemone at all to me. Some of them come in a lime green color while most come in a redish/purple color which it looks like you have. If you can, feel it and let me know if it is very very soft to the touch because that is how ours are, and they aren't very slimy like most of our other mushrooms. Also if you will feed it and see if it rolls into a ball around its food. Our biggest one will roll around food in just a few seconds. If it is the bubble mushroom you got a nice freebie!!!!!!
