Sick Tuxedo Urchin?

[dapoint23]

My Tuxedo Urchin has been very healthy but he suddenly seemed to take a turn for the worse. His color is not nearly as bright and it appears some of his tentacles are missing. He's not carrying things around as much as he used to either. Is this typical or what might I be doing wrong?

 

[Reefer577]

Starving to death maybe? Do you still have plenty of green algae in your tank? Ph/temperature changes could also be the culprit.