Depending on the case it would sometimes be Pyrarum, Pyris or Pyras.
That you said Greek. ;Pfrom the greek language point of view, your right, but where is the fun in that?
I just pretend the singular form actualy ends in an S, which got silent over time and then vanished in writing too, but it follows the example of der Atlas/die Atlanten still. So, die Pyranten.Edit: or as it's product of Germany, probably Pyra(?) is correct.