it looks like a bta, but a very, very sick one. its lost its zoolanthae due to stress or sickness and if you want it to live you will have to hand feed it tiny amounts of seafood protein-- slivers of silversides or mysis shrimp, as often as 2 times a day for a week or two, then at least three times a week... if it makes it that long.
any anemone that's white is very ill...