A prasinophycean alga of the genus Cymatiosphaera in the Early Devonian Rhynie chert

Spherical phycomata of prasinophycean algae are preserved in the Early Devonian Rhynie chert. Because they display a surface reticulum composed of muri oriented perpendicular to the vesicle surface, they are assigned to the genus Cymatiosphaera (Cymatiosphaeraceae, Pyramimonadales). We interpret the size range of the phycomata (24 to 48 μm in overall diameter) as reflecting continued metabolic activity and growth of the alga during the phycoma stage. The phycomata from the Rhynie chert represent the earliest account of the genus Cymatiosphaera in a freshwater paleoecosystem, and broaden our knowledge about the ecological diversity of Early Devonian prasinophycean algae.