That's not the foot you all are seeing - it's gastrovascular cavity (i.e. the "guts") are completely everted. That anemone is sitting right-side up with its insides sticking upward.
And, it's not splitting - M. doreensis (LTAs) don't split. It's extremely stressed, and prognosis is poor, unfortunately.
Also, M. doreensis is a sand-dwelling anemone and will like to bury its foot in sand - but... it will likely need to invert before it does that, but... perhaps adding some substrate will make it feel more "comfortable" perhaps - I don't know really.
Cheers
Mike