I can't tell with yours, but I've had small little crabs come with a piece or two of my monti's as well, and I think they were acro crabs.  They were mostly pinkish/white with black masks and black claw tips.  They were a good crab, I was told. 
		
	
		
		
		
		
			
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				65 gallon mixed reef and 34 gallon mixed reef
			 
		
		
		
		
	
		
		
	
	
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