This is an Orange Ball Anemone, supersized with a macro lens. Usually they are about 3/8" in diameter from tip to tip.  This was a bigger one, maybe 3/4" in diameter. I have them throughout all my tanks, and they are opportunistic filter feeders. I think they are quite pretty, and study the rockwork after lights out with a flashlight to find these little guys wide open. During the daytime I hardly see any.