That is a Majano Anemone. They're bad, REALLY BAD, IMO (and almost everyone elses). They normally can be plucked right off the rock, they don't have a strong base like some anemones do. For the ones that I can't pluck off, I use Aiptasia-X, it's readily available at most LFS's lemon juice, boiling water and a Kalwasser paste never works for us. Aiptaisia-X kills them quickly, most of the time. The only thing that sucks is you have to be quick when you try to feed them the poison, they close up very fast, whereas Aiptasia actually try to eat the stuff. I normally try to get as much into the oral disc as possible and then once it closes up I stab it and inject more and cover it completely, it seems to be the only way to get rid of them. Just make sure when you kill it, you turn the pumps off for a little bit. Get rid of it ASAP, they multiply really fast and can take over corals. I had one on a candycane coral, it multiplied and took over the rock, I just couldn't get rid of it all at once and it eventually destroyed my candycane.
Good luck