These beautiful creatures are a species of isopod known only by their scientifc name Porcellio expansus. In the wild this species is found in southern Spain.
Here in the UK we tend to refer to our native isopods (most of which are grey rather than the lovely colouration of this species) as woodlice, although depending on where you are from they are also known by dozens of other weird and wonderful local names including roly-poly, cheeselog, granny grey and chucky pig (which is what I personally called them as a child)! This species is particularly beautiful as you can see here:
These individuals have grown a lot since I first bought them, when they looked like this: