Contrasting classes of superconductors

I think the Figure below is a really nice one which compares the variation of the superconducting order parameter on the Fermi surfaces for four different classes of superconductor:

a. elemental

b. cuprates

c. MgB2

d. iron pnictides

The figure is taken from a 2010 Perspective in Nature by Igor Mazin.

A recent post considered how to unify b. and d.