Looks like the bad kind of anemone called Aiptasis. If it is, they sting. Use the handle of your net and try to touch it. If it is, it will retract when you get near it.
Aiptasis anemones are a pest because they sting you and other animals in your tank, and they are VERY invasive. It is a hitch-hiker, and I have read they can spawn 600 or more at a time. I hope I'm wrong, I am dealing with that problem myself. I have tried cutting them out, next I will try Peppermint Shrimp.