looks like xenia or anthelia to me. do the polyps pulse? my xenia keeps melting and recovering. when it melts it leaves a mat that looks exactly the same and the new xenia grows out of it.
My guess is that it's star polyps. After a few days in your tank, the polyps should start to come out more. When healthy, they'll look like a waving patch of grass. In this case, probably light purple grass.