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. 
		
	
		
		
		
		
		
	
		
		
	
	
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