Minimax or amplexidiscus??
 

Hi we have a green mushroom-like thing in our tank which recently tried (and failed thanks to quick action from us!) one of our baby clown fish. I originally thought it was a rhodactis mushroom, then on attempting to munch the fish thought maybe it was an 'elephant ear' amplexidiscus mushroom. However someone in a reef shop recently suggested it was a minimax carpet anemone. Any easy ways to tell them apart?? It is sticky to the touch unlike the other mushrooms in the tank, has a fringe of short tentacles around the outside, appears to be photosynthetic in that it reaches up round the rocks to get at the light, doesn't move around the tank, and reacts amazingly quickly - much much faster than any of the other mushrooms - to touch or feeding. The clown who got caught was covered in a white mucus for a couple of days after and very dazed but has now recovered completely :-)

Wow, I have half a dozen minimax anemones and none of them has ever made a move on anything alive in my tank. I've even had a few very small bait fish in the tank that were there to be food!

A photo or two, or even three would probably be a big help.

How big is it in diameter?

It does ound like a maxi mini carpet nem by your description, but pics will help confirm.