Pterocystis anapoda  Siemensma & Roijackers, 1988

Diagnosis: Cell diameter c. 12 µm. Spine-scales 6.5-10.6 µm long, shaft 0.21-0.26 µm in diameter, cylindrical, hollow, with a blunt apex; proximal part of the shaft strongly bent; shaft with a membranous base divided in two wings; base 2.4-3.0 µm long and 1.6-2.5 µm wide; its trapezoid shape resembles a spade or duckfoot; laterally these wings show a slightly convoluted marginal area which becomes distally broader; upper surface of the basal membrane is fairly smooth, at the lower surface the shaft is pronounced with a slight indication of radial ribs on both sides of the shaft; some spine scale membranes show a slight basal depression.
Plate scales are 3.8-4.1 X 1.8-2.8 µm, broadly elliptical to ovoid, with a central depression with one longitudinal rib and several radial ribs; surface of the plate-scales smooth, with a small marginal rim.

Remarks: The specific name refers to the duckfoot-like structure of the spine scales. This species has been collected once in large numbers from a small eutrophic ditch near the town of Bolsward in the northern part of the Netherlands.
Pterocystis anapoda shows some resemblance to Pterocystis pinnata but differs from the latter in the shape of the spine-scales:

1. the apex of P. pinnata is rather sharply pointed while the apex of P. anapoda is abruptly cut off;
2. the basal membrane of P. anapoda is more or less flat while that of P. pinnata shows a deep tapering depression;
3. the wings of P. pinnata extend along the shaft and terminate subapically, whereas the wings of P. anapoda do not extend along the shaft;
4. the shaft of P. pinnata is rather straight whereas that of P. anapoda is strongly bent.