Rhizaspis simplex Skuja 1948
Diagnosis: test a flexible, colorless, hyaline membrane, ovoid or elongated oval, strongly compressed; test in cross-section flattened; test smooth or with two distinct longitudinal rounded keels; aperture slit-like, between folds and flexible; plasma fills the test completely; nucleus large, with single nucleolus; filopodia long and branched. Longitudinal division.
Dimensions: Length 46-62 µm, width 22-35 µm
Ecology: Freshwater, sediment. Marshes, Letland.