Those are tulip anemones. I am not sure of the scientific name. I have a herd of them in my tank. They get to be about as big as a quarter in diameter. They grow pretty quick and split quickly. I started with 4 I think from Repto and now have around a dozen in about a year. They typecially stay in one place but will wander. They seem to have a pretty powerful sting. They have nuked a shroom and some zoas growing near them. I am trying to keep my population in control by trading them.