Genus Pterocystis Siemensma & Roijackers, 1988

Diagnosis: Centrohelea with a periplast with tangential plate scales and radial scales; radial scales consist of a shaft and a thin, membranous basal region which may extend along the shaft and may form a stalk-like protrusion at the base of the spicule. The membranous region is not clearly differentiated into lateral and basal regions as in Echinocystis.
Type species: Pterocystis pteracantha (Siemensma, 1981) Siemensma & Roijackers, 1988
Reference: Mikrjukov (1997).

Though it is very difficult to identify heliozoans light microscopically, it is still possible to identify the genus and sometimes the species. It might be helpful to dry a specimen. These dried scales are probably from Echinocystis erinaceoides.
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