these are pretty primitive creatures...and they do chew up things like coral substrate, sand, etc...anything that may have algae or organic debris. 
 
Feeding sea urchins  some dried seaweed (non flavoured , non salted kind) is fine...but supplementing that with fish food tabs once in a while would be great also. 
		
	
		
		
		
		
		
	
		
		
	
	
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