makoJ I have a similar one and it was labeled as a acanthastrea hemprichii when I bought it a couple years ago. I still believe it to be a hemp in comparison with others alike.
The ishi on my website that ikuwaseven is referring to has much smaller heads and grows different then the hemprichii. When comparing the 2 side by side you can see the difference.
Make sure you keep it low in the tank, they can shift colors if blasted with light.
Ciao, Jen=)