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Pterocystidae  Cavalier-Smith and Von der Heyden, 2007

Diagnosis: Periplast ancestrally with two contrasting types of siliceous scales:
1 Tangential plate-scales (margin not hollow and inrolled but sometimes thickened) oval, sometimes slightly (rarely markedly) narrower at one end, sometimes slightly indented on one side (rarely slightly on both) but never distinctly bi-lobed;
2 Bipartite radial spine-scales typically consisting of a leaf-like blade with an axial rib, usually extended apically as a projecting needle-like point (blunt or pointed, but not branched), and lateral wings; radial scale-base may be rounded or truncated and may be in the same plane as the blade or somewhat bent away from it (Pterocystis) or markedly extended as a distinct shelf or basal disc (sometimes called basal wing: Mikrjukov, 2002) orthogonal to the main blade (Raineriophrys); species with a pronounced basal wing may have lateral wings that are greatly reduced or absent; if silica scales are rarely secondarily missing (Chlamydaster), the cell has a distinct mucous coat; funnel-shaped scales absent.
Type genus: Pterocystis.
   
Included genera: 
   
Pterocystis  Siemensma and Roijackers, 1988
Raineriophrys  Mikrjukov, 2000
Chlamydaster  Rainer, 1968
   
The distinction between Raineriophrys and Pterocystis is not sharp; molecular and ultrastructural investigation of all other Raineriophrys species is needed to check whether Raineriophrys is monophyletic and deserves generic distinction.

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