+1^
It's a pretty common (very fast growing & extreme spreading) coral Pulsating Xenia.
It might be difficult to keep it from taking up more space than most people want it to from what I've heard.
+2 it grows like a weed but I love it because it adds movement to my tank. A lot of aquarists use it as a "monitoring' coral because if something's wrong with the water parameters this corals will be the first to show signs of stress. A helpful link about xenia I read awhile back http://www.kierondodds.com/uploads/Xenia.pdf
Keep in mind it will spread readily onto any solid surface (including the glass of your tank) if tank conditions are right. I highly suggest keeping it on it's own completely segregated rock. I'm speaking from a LOT of first hand experience here. I had a tank almost completely dedicated to Xenia for over a year. It helped my "hobby" to pay for itself in Xenia frags
That Xenia is less invasive in my experience. The walking Xenia will take over much quicker. As long as you 'prune' your xenia when it starts to get too big, you will have no problems. Just think of it as a shrub.