Your impression that this mite is a member of the Pygmephoroidea is correct; it is not a member of the Pyemotoidea, which has a subtriangular trochanter IV.
Working through the key in the latest Manual of Acarology, from couplet 58 on page 325, you can see: femur & genu IV separate (not Tarsonemoidea); tarsus I with single claw (hard to see in photo, but seems present, so it's not Dolichocyboidea); trochanter IV quadrangular, different from trochanter III (not Trochometridioidea or Pyemotoidea); prodorsum not covered by tergite C = not Scutacaroidea, is Pygmephoroidea.
I cannot see enough to reliably identify it a Siteroptidae or Pygmephoridae (or Neopygmephoridae, which is also sometimes recognised).
Iran also happens to have one of the world's experts on the Heterostigmata in Hamidreza Hajiqanbar, based at Tarbiat Modares University. He'd be able to give a good identification if you need further information.
It looks very much like Pediculaster bureschi (Savulkina 1978): the pro and poststernal apodemes proportions and shape; the dorsal seta distribution; vi and ve related to capilate sensillum; the fourth and first legs. Take a look here.