Well I am not completely sure, you've done me there. I regonize the ray but can't quite put a name to it and it is hard to tell from the pic, at first I thought P. reticulata but the markings aren't quite right. CFC should be able to remind me when he gets on, don't worry we will get to the bottom of it.
As for 8" you need to learn that the lfs will bend the truth to get you to buy the fish. I assure you there is no variety that only grows to 8" f there were it would be extremely popular but alas rays that small don't exist or at least not in numbers that your lfs could get ahold of them for under say $250 Don't worry everyone has had an lfs give them bad info.