It sure looks like a Trapezia rufopunctata also known as the "coral crab". But i dont think that's what it is although they closely resemble eachother in shape. If you compare your crab with a Trapezia rufopunctata, you will notice the spots on a Trapezia rufopunctata are small and red. From the picture you have displayed, that crab appears to have large white spots. That's the difference. Whatever it is, your very lucky to have gotten such a nice looking critter like that by mistake. It's too bad they dont sell those at LFS or on the net, i'd definately buy a crab like that if i could get my hands on it. But unfortunately they aren't commonly available in the trade.