Don't know what this is but it is reddish in colour with a green center that shows up really good under my blue marine light. It has little tentacle sticking out that you can't see in the pic and they move and look like there are tiny balls on the ends of the tentacles. At night is shrinks up smaller but in the daytime when the lights are on in the tank it gets much bigger. It's only about maybe 3/4 " across at it's biggest. It stays in the same spot though.
