I had a star do the same thing. It will eventually just become the center with no legs. I agree with moving it to another tank though, just in case.
I've found most starfish to be very very fragile and not do well in the home aquarium. They do not do very well in newer tanks especially. :-(
The only hardy star i have ever had is the sea serpent ones, they come in several colors too so you might consider that if you want to replace this one.
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.