Pterocystis pinnata  (Nicholls, 1983) Siemensma and Roijackers, 1988
  
The observed specimens were as originally diagnosed. Cell diameter ca. 8 µm. The spine-scales measured 3.6-5.5 µm with the basal membrane ca. 1.8 µm broad. The depression formed by the membrane and the basal part of the shaft looks like a hollow pyramid with rounded edges.
The observed specimens were collected in Sweden.