Rhizaspis arcuatus (Penard, 1902) (= Pamphagus arcuatus)
Diagnosis: test ovoid with a flexible, colorless, hyaline membrane; fundus tapering into a more or less sharp point; test in cross-section flattened; aperture usually between folds and flexible; plasma fills the test completely; nucleus vesicular or ovular; filopodia usually few, long and strait.
Dimensions: 86-90 µm
Ecology: Freshwater, sediments.
Remarks: I don't think that this is a separate species, but identical to P. scutigera.