I'd like to see a better pic of it. I've seen a lot of aiptasia and majano anemones in my time and that looks more like a ball anemone which is pretty harmless and won't spread like aiptasia or majano.
You can kill it to be on the side of caution, but I wouldn't. I'd want a better view, a better picture and solid ID. Have you gone online to see what an aiptasia looks like? Then google a ball anemone and compare it to yours. You get to see your little guy with your own eyes, so you can do a better comparison than we can from one... less than perfect photo.
Just my 2 cents worth.
I may be wrong, but it's not like this is a dire emergency even if it is an aiptasia.