Assulina muscorum var. stenostoma  Schönborn, 1964

Diagnosis: Shell hyaline and transparent. Idiosomes as in the nominate form. Shell shape highly variable, but always with an extremely small pseudostome, which may still be oval but is usually round. No protruding mouth scales. In lateral view, the shell is longitudinally oval or curved to one side. Protoplasm as in the nominate form.

Dimensions: Schönborn (1964): Shell length 30—40 µm; width 20–30 µm; pseudostome 0.5–3.0 µm.

Ecology: Common in pine and birch forest soils.