Yeah, I am not a fan of Brittle stars either...too opportunistic. We had one take a gorgeous baby Dragon Wrasse within hours of adding it.
For us, we added our Brittle Star because from all we read they were great detrious cleaners, etc. We found this to be true when he was small, he would come lumbering out at feeding time and clean up everything on the bottom and he would come out at night. However, once he got big and fat, he didn't come out at all...just stuck arms out and let food float into them. After he ate the Dragon Wrasse we evicted him.
Sorry for the loss of the Shrimp...that's lame.