It's
Corynactis or
Psuedocorynactis sp. I always get the two mixed up but it's one or the other. I think of them as anemones but I guess "coralimorph" is the more correct term.
Here's an article where they are discussed:
http://www.advancedaquarist.com/issu...002/invert.htm
Scroll down to the bottom or do a search on "corynactis" or "orange ball".