I had one of these in my tank for about two weeks (although it had 5 legs) and one day I noticed that it all of a suden was gone, I now have 1 leg hanging on my glass, I have talked to a few people that have told me that the one leg will grow in to a full star, but I am not holding my breath.
This guy had 4 arms to begin with, with slight damage to one of the arms. In the couple weeks since this photo, the damaged arm has completely dissolved and the rest of him doesn't look too great. Through my own dumb-assedness I acclimated him all wrong and I think I'm paying the price for it now. :-(