Toddpolish, I had one alot bigger than your pic, just stuck him with about 3 mil of boiling water and that was the end of him. The others I had were about half that size.
Just would like to also pass on that I was in a lfs and they have a 55 gal reef tank. Well I noticed about five or six aptasias. About three weeks later went back in and I could not believe it. The tank was totaly full of them. Keep a close eye when you kill em, I read they put of offspring nearby.