Moon Crabs?

I can't find a whole lot of info about these guys. My brother just called me asking about them because evidently they got my nephews two. Being the 'oddity' in the family I get the questions such as this.
I know nothing about them other then they are attractive little boogers, I was hoping some of you might help me out.
I already lectured them on buying something they know nothing about but..brothers will be brothers. Even at 35.

Great colorful pets.Keep them the same way as if you were keeping a hermit crab.
My son has one. It is in a 10 gallon tank with sand, a water bowl (with the hermit crab sponge) and a food bowl that I put pellet food in for it to eat.
It is at room temps and doing pretty well.
Any idea where he found them? They are not too common and you usually have to order them online.