It appears to be a species of Echinometra. While they are harmless to fish and other members of your cleanup crew as they mostly consume algae, they will erode your rockwork by boring holes in it, causing collapses that can wreck havoc with your corals.
Looks like Echinometra? They are ok they eat algae, some can eat coraline algae as well. Watch out for the spines they make nasty wounds. To learn more about some common hitchhikers you can look on the hitchhiker page in the library on this board.
i've already looked at the hitch hikers faq but i wanted an expert opinion because i dont want it doing damage of some sort to the tank. another thing its kind of funny because i have not bought any live rock for a few years, hmmm
Its actualy touch and go with urchin identefication .
SOme species of spiney urchins that look like your EAT coral, not just algae and rock.
Iwould try to get a better full bodied pic before deciding If I were you.
I will concur with genus Echinometra. I had a bunch of some kind of Echinometra at one point. They did rasp algae right down to bare rock but I never saw them bore holes, (although that certainly does not mean they didn't, I had a lot of rock at the time, their common name is the "rock boring urchin" I believe).
They did a fabulous job on some dense turf algae I had growing on my clam, cleaned both halves of the shell and had it looking white and brand new!
