One of a dozen corals often called "pineapple coral," or "moon coral," but there is a specific name for it...which always eludes me. Don't know why I can't ever think of that word...
It's a relative of the maze brain, which has sweepers up to 6" long, mostly overhead, as well as the small fuzzies that come out when there's food in the tank, so be careful what you set it next to.
What's that word, guys?