It looks an Echinometra spp. to me. You can find more information about themhere. Saying that though, those are the sort of questions you need to research BEFORE buying a new tankmate.
As long as if you have plenty of rockwork for it to rasp on and I'd suggest a minimum of 50gal tank you should be OK. The are mainly herbivorous but will eat meaty foods. They need excellent water conditions.
They do drop spines but mainly as an indictaion to poor health/conditions.
If it were me, I'd take the urchin back with you. Does your avatar picture show your current set up as it is. Is that the amount of rock you have, what's in the picture?