Brittle Star eating Hermit Crabs ?

[Plesoine]

Every time I try adding Hermit Crabs or Shrimp they disapear in a few days. Its a 180 gallon reef tank. I have some large Tangs but never heard of them doing this. The only thing I can think of is a Brittle Star Fish ? Any thoughts ?

 

[Peace River]

Typically brittle stars are scavengers that go after dead, dying, or otherwise compromised creatures. Is it possible that the crabs and shrimp were molting? Otherwise it is less likely that it was the brittle stars.