Man these things freak me out. I've got plenty of micro brittles and other detrivores so I don't think these big ones are worth the risk.
The arm is well attached won't sever off or anything if you pull on it. If it does though... just keep pulling the other arms and then remove the main disc . You can glue it back together later. In my case, I removed mine with just a net... Since my rock is elevated it was easy to poke the star repeatedly till it came out into the open. I think luring it out with food will work as well.
I agree. Just put a silverside or some sort of carnivore pellet in your hand and he will come right out and attack you. Just kidding. Have fun. My green one is a little over 20in across now and will crawl in my hand for silversides.
He is prob about to go too.