Rhogostoma minus Belar, 1921
Diagnosis: Flexible, smooth inorganic test, with aperture from which radiating lamellar, fingerlike, non-granular, branching filopodia constantly extend and retract at all angles; shape a strongly laterally flattened prolate ellipsoid projecting vertically from substratum;
Cell fills test completely. Cleft-like aperture beneath the cell hard to see in life, opening towards substratum; pseudopodia emerge through the cleft, can extend many times body length and pull the cell along the substratum; cell pulled over leading pseudopodia as trailing pseudopodia retract, progress smooth. Refractive granules; several small vesicles; large lateral contractile vacuole; nucleus usually central. Form groups of several cells. Divide by binary fission.
Dimensions: Cell broader diameter seen from dorsal end: 7.3 µm (6.5-8.5 µm) in living cultures when rapidly growing (can be 10-12 µm in old stationary cultures).
Ecology: Freshwater. Heterotrophic.
Remarks: Freshwater species of Lecythium are 3-10 times larger.
All information from Howe et al, 2011