Had this carpet since May 2004. I've been "100% certain" up until today that it is
Stichodactyla gigantea. Today I just noticed it do something that I've never noticed it do before that makes me question my ID and now I wonder if it could be
S. mertensii. The longer tentacles surrounding the mouth is a classic merten's feature. (And if it IS a merten's ... hoo boy do I have a problem down the road, in terms of diameter they are the largest hosting species of anemones ...

Forget the ritteri, these get BIGGER!)
Funny that it's never done this before.
At the moment it is a nice sort-of compact 8" in diameter.
For reference, here are some older pictures:
When it was first purchased (May '04):

And after about a month (June '04):
