Pterocystis polymorpha Cavalier-Smith and von der Heyden, 2007
Diagnosis: radial spine-scales (3-4 µm) non-striated, lacking transverse ribs, polymorphic, ranging from ovate without a pointedtip (axial rib falls short of apex, unlike P. ovata), but midrib not extending into a long drawn out cuspidate tip, and dense thickening well away from the base of the scale (about one third along its length), which is
much more distinctly rounded than in contorta, to very different strongly cuspidate scales where the tip is much more strongly twisted to one side than in P. contorta.
Tangential plate-scales (1-2 µm) markedly asymmetric, almost flat on one side, with central axial ridge, but no radial furrowing.
Distinguished from P. ovata by its more strongly asymmetric plate scales and the non-cuspidate radial scales having more rounded tips.
Type locality: lake sediment, Priest Pot, Cumbria, UK.