Black Brittle Starfish Question

[Madreefer]

I got a black brittle starfish as a hitchiker about 10 years ago. It started out to be the size of a dime and is now rather big. It has always lived in the same rock even after several tank swaps and "tank renos". For the last 2 days it has been in the middle of my tank not moving. There is no sings of any of it's arms deteriating and the tentacles are still on it's arms. I'm contimplating taking it out. Does anybody know the lifespan of these or have any suggestions. I know Whatcaneyedo just had a green brittle that died. I did flip it upside down and left it for a couple of hours and it did not turn itself over.