I have three long-spined black urchins.  One that hitchiked in with the rock.  I suspect that they do eat some hair algae, but I wouldn't say they seek it out.  I think they'll eat coraline as well. 
		
	
		
		
		
		
			
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				400 gal reef.  Established April, 2007.  3 Sequence Dart, RM12-4 skimmer, 2 x OM4Ways,  Yellow Tang, Maroon Clown (pair), Blonde Naso Tang, Vlamingi Tang, Foxface Rabbit, Unicorn Tang, 2 Pakistani Butterflies and a few coral gobies
 
My Tank:   http://www.canreef.com/vbulletin/showthread.php?t=28436
			 
		
		
		
		
	
		
		
	
	
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