Genus Rhizaspis Skuja 1948 emend. Dumack et al, 2017
= Plagiophrys Claparède & Lachmann, 1859
Diagnosis: Thecate amoebae with ventral slit-like, but flexible, cleft that emits filopodia; theca thin, flexible, in active cells adherent throughout to cell surface, with exosomes (R. parvipunctata) or without (all other species), sometimes deformed by ingested food, often wrinkled or folded, consisting of single smooth dense layer outside and scarcely thicker than the plasma membrane; thus with bilateral symmetry (ventral flattened). Round nucleus; nucleoli may be visible by light microscopy, often one, sometimes several. Cells may be divided in zones (basal to apical): several contractile vacuoles, food vacuoles, nucleus embedded by a large number of in size varying granules. Inhabiting fresh-waters. Eukaryvorous, mainly feeding on algae, especially diatoms. Division longitudinal, binary. Sexual reproduction unknown.
Type species: R. granulata Skuja 1948
Most species are hardly distinguishable by light microscopy. A main character might be the presence of one central nucleolus versus several nucleoli.
|1||Test with a median rib terminating into a sharp point||R. arcuatus|
|–||Test without median rib||2|
|2||Nucleus with central nucleolus||R. granulata|
|–||Nucleus without central nucleolus||3|
|3||Test without rib or wings||4|
|–||Shell with distinct keel or wings||5|
|5||Edge usually smooth||R. scutiformis|
|–||Edge with many wrinkels||R. marginata|