Based on your statements about the red base, along with the 2 pictures above, I would now lean more towards LTA, or Macrodactyla Doreensis. In the last set of pictures, the underside appears smooth with rows of dots called veruccae. This all fits the M.Doreensis decription very well, but again, they do not come in white. This anemone can't be naturally white unless it is non-photosynthetic (which I doubt).
Malu and Crispa have more random verrucae, not in vertical lines like LTA.Ive seen a bleached H.crispa that looked almost identical to this.
Hmmmmm
That look like the column of a H. crispa, not M. doreensis