I don't think that is a blastomussa (although that would be the best guess as it looks similar to a blasto). But there are indicators by the way it is growing and the polyps that make me think it is not.
I can't id it though. The LPS forum may be able to help.
eitherway, definately not a blastomussa wellsi. It appears there are small "stalks/branches". if it is a blasto it is a merleti.
eitherway that is a VERY nice piece.