Hyalosphenia penardi Lauterborn, 1908
Diagnosis: Shell transparent, colorless, yellow or brown, elliptical with a strongly curved, nearly semi-circular pseudostome; fundus broadly rounded; surface without structure; plasma usually partly filling the shell, with some epipodia; shell strongly compressed, especially towards the aperture; nucleus globular with a number of spherical nucleoli.
Dimensions: L 180 µm, B 70 µm.
Ecology and distribution: This species has been found in the Upper Rhine in Germany, between diatoms, by Lauterborn, and, unless it is a new species, in the Netherlands by Cagri Yalcin. Food: mainly diatoms.
This species was (probably) rediscovered in the Netherlands in 2021 by Cagri Yalcin who published the video below on YouTube. Probably, as it could also be a new species, as there is a narrowing, a kind of neck, above the aperture and the shell is clearly dotted.