Rhogostoma schuessleri Belar, 1921
Diagnosis: Cell in dorsal view spherical to elliptical, sometimes slightly narrowed, 8-shaped, at the aperture end, surrounded by a semi-rigid colorless, hyaline membrane or pellicle; aperture a small distinct cleft, with can widen to let pass food; plasma fills the test nearly completely; filopodia long, tapering and straight, branching, without granules. Cell may form conspicuous lamellipodium broader than the cell, from which filopodia extend. Nucleus not observed. One to two small contractile vacuoles. When travelling, cell occasionally tilts to point cleft in direction of travel (see micrographs) of leading pseudopodia for locomotion.
Dimensions: larger than other known species: ca. 15-21 µm.
Ecology: I found this species in a freshwater lake, the Spiegelplas, and in Sphagnum along the Bert Bospad, all in the Netherlands.
Remarks: This species is hard to distinguish from Lecythium species. Caracteristics are the apertural cleft and the slightly 8-shape, though not always present.