Urchin trouble?

I'm wondering what's causing the problems that I have with zoas and polyps going missing.
About a month ago, I got a nice frag of some incredible zoas. They opened immediately and looked great. By day 3, the frag plug was empty. I saw my urchin right next to them the night before.
Yesterday, I got a nice rock with maybe 20 yellow polyps and tons of different zoas on it. Again they extended right when they were placed in the tank. This am before I left for work I took a look and the rock was empty.
I'm getting annoyed and I wonder if the urchin is to blame. Any ideas or opinions?

 

What type of urchin?

 

Thats way dissaponting. By by urchin.

 

Yep need to know what kind of urchin. Some are not reef friendly. Some species will either straight eat soft coals or some will steal them to try to attach to themselves for camouflage. You may also have a nocturnal hitch hiker doing it as well. I had bristle worms destroy a bunch of coals and clams before I figured out what was going on. A late night recon may be needed.

 

It's a long spine with the blue diamonds on it's body.