It's a type of octocoral (8 arms) and it grows like weeds in my system. I have two different brown varieties. The blue colored octocorals are much more difficult. It seems to be pretty tolerant of my other corals, but fights with my mushrooms for space. I have to remove big clumps of it occasionally or it would dominate the reef. I really like it because it adds movement to the tank and the clowns love to host it. I can't stand anemones (personal preference), so this is a good replacement for them.