From the FAQ:
Q: I have a small anemone looking critter that is about 1" or so in diameter with short stubby tentacles, and what might be bubble tips. Is this an aiptasia or did I get lucky and get a baby bubble tip?
A: You probably didnt get as lucky as you think, cause it probably is Anemonia majano , a small anemone which most people consider to be a pest. In most cases, this anemone can reproduce quickly and spread thoughout the tank, and like Aiptasia, can sting its neighbors quite badly. It's unlikely that you will find a biological control such as peppermint shrimp for these, however you probably will have better luck using an injection of limewater if you find that they must be controlled in your tank. For further reading, you can check out Terry Siegel's Article on Aquarium Frontiers where he describes his use of Chaetodon lunula for control of Anemonia (which should only be used in extreme cases in this author's opinion).