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).