Pterocystis kilianii (Dürrschmidt, 1987) Siemensma and Roijackers, 1988
Diagnosis: Periplast 25-40 µm in diameter; details of protoplast unknown. Scales of two types. Spine scales 5-10 µm long, usually conspicuously curved outwards in the proximal quarter of their length. They consist of shaft, lateral wings and basal wing. The shaft is hollow, 0.23 µm thick throughout, abruptly cut off at the apex at right angles without taper, basally terminating with a “shovel-like” structure formed by the wings. There are two lateral wings in an almost V-form arrangement relative to the main axes of the shafts and a basal wing, which spreads between the ventral edges of the lateral wings. The lateral wings are 4.8-8.0 µm long, accompanying 2/3 of the shaft length. They taper distally. Cross ribs are present on the lateral wings and on the basal wing. Plate scales, 2.6-4.3 X 2.1-3.2 µm, are ovoid or elliptical, patternless, except for a subvisible axial thickening.
The cell diameter of the observed Dutch and Swedish specimens was ca. 14 µm. The spine-scales are 7.0-8.4 µm long. Their basal membrane is ca. 1.8 µm wide. Specimens from the Swedish material had spine-scales with broader wings than the Dutch specimens. Sometimes the edge sof the lateral wings were highly wrinkled, though smooth wings were found among wrinkled ones. Lateral folds or wrinkles cannot be used as a taxonomic character.
Remarks: P. kilianii bears some likeness to P. pantopodeoides Nicholls (1983, syn. A. cuneiformis Dürrschmidt 1985) and P. fortesca Nicholls (1983), having ribs on the basal wings, and non-tapering shafts. Distinguishing features are the longer and gradually tapering lateral wings, the shorter shafts, and the patternless plate scales.
P. kilianii is also similar to P. erinaceoides especially as regards the wedge-like shape of the spine scale basis. To distinguish between both species offers no problems. The most useful characteristics are the absence of any kind of ribs on the wings, the tapering shafts, and the presence of a central swelling on the plate scales. However, EM is necessary for reliable identification.
Distribution: Chile, Germany, the Netherlands, Sweden.