There are many, many kinds of aiptasia/glass anemone. I had 2 just like yours. If you spend enough time scouring photos on the net you can find them. They don't seem to spread like the common brown ones we always see. I left them alone and have not seen them since we moved. If I were you I'd just keep an eye on them. If they start making you nervous, then nuk'em.
Very nice pic, BTW.
ps...this isn't the easiest site to navigate, but they do have a few pics. If you scroll down below the pics on this page there is a small list of other aiptasia. Just click on them and scrll down to see if they have a pic of it. I bookmarked this a long time ago and forgot I had it.
http://zipcodezoo.com/Animals/A/Aiptasia_mutabilis.asp
Also search for aiptasia pallida, or pale anemone