Angie,
I had a pencil urchin (similar in habits to your pincushion?) in my 65 reef tank for about a week, until one morning, I found him with a pulsating xenia in his "beek". :eek: He had ripped it entirely from the rock and appeared to be eating it. :mad: So I plucked the coral from his mouth and removed him to my fish only tank where he is happly moving aorund grazing on the live rock. The xenia was replaced back on the rock again and did amazingly survive the ordeal.

I didn't know any urchins were totally reef safe.