what am I?

Nope, you definitely don't want them in any tank. Keep in mind though that like most hydroids, these anemones have a free floating planktonic stage so boiling the rock doesn't guarantee anything if you put in back in a tank with the "old" sand, water, decorations, etc. When I break down my existing tank and start new, I plan on starting the tank completely "sterile" except for whatever corals I decide to keep. I am never going to take the risk of having these things take over again