Glass anemone are the same thing as aiptasia, and they will spread. If this is in a reef tank, you'll want to remove them because of the threat they pose to your corals.
If you can find a peppermint shrimp, and it is compatible with the other members of the tank, they will take care of the small ones. If you have any large ones, you'll need to treat them with kalkwasser (create a soupy paste and inject it into the trunk), or boiling water. Do not try removing them manually--this will result in them spreading.
We have a few in our FO, and they've increased their numbers a bit, but nothing overwhelming. Since a shrimp is out of the question in this tank, we'll being using kalkwasser sometime in the next few weeks.