The local and long-range bulk liquid structures of four primary alkylammonium protic ionic liquids (PILs), ethylammonium hydrogen sulfate, ethylammonium formate, ethylammonium thiocyanate and butylammonium thiocyanate, are determined using neutron diffraction and computer simulations and compared to those determined previously for ethylammonium nitrate and propylammonium nitrate. All these PILs arrange into a sponge-like bicontinuous nanostructure consisting of polar and apolar domains. Lengthening the cation alkyl chain leads to nanostructures where the polar and apolar domains are better segregated, with the ions in more precisely defined positions relative to one another. Changing the anion (for the same cation) has comparatively little effect on structure. The reason all these PIL adopt low curvature sponge-like morphologies, despite the marked changes in the cation and anion structures, is because the preferred areas of the non-polar and polar fragments within the nanostructure are similar.