Help with Unknown Predator

[Green Phantom]

I think it looks like a bristlestar tentacle and it's brown. I think I've seen it in my live rock one time. As soon as I looked at it, it disappears into the rock. I'm not sure if this is what killed the fish. I remember now that when I first set up the tank, there was a shrimp I saw not sure what kind but it was brown. Haven't seen it since...could be what is killing the fish. I believe it was from some Cuban liverock that I purchased from King Ed.

Heading down to the tank to take a look...hopefully I'll see something with the flashlight.