Well it isn't aptasia, it might be a crop of xenia starting to grow, time will tell what kind of coral it is when it gets a little bigger...It's pretty.
I think the base is different...Xenia has a longer body before you see the little flowers/hands, while these seem to be flush with the rock. That's why I said time would tell because I couldn't see the body of the coral.
They're pretty much like most polyp-type corals...if they like your tank, they'll multiply. They don't "pulse" or otherwise move (other than to open and close), but they're pretty.