Nadinella tenella Penard, 1900
Diagnosis: shell ovoid or pyriform, in cross section circular, narrowing towards the pseudostome into a distinct neck; aperture broad elliptical, surrounded by a thin hyaline outward bend collar; shell composed of an organic material, embedded with mineral grains of different size, usually not covering the surface completely, with larger grains embedded in the fundus part en smaller grains towards the aperture; the collar is free of grains. Nucleus globular. Filopodia very long and thin, usually one to three. Plasma doesn’t fill the shell completely. One known species.
Dimensions: Penard 50-55 µm, my measurements: 39-60 µm (n=5).
Ecology: Clear fresh (running) water. De Groot (1979) found this rare species in small clear streams in the Netherlands; Torök found this species in running waters of the Danube in Hungary. I collected this species from a very shallow forest ditch in Gaasterland, in the northern part of the Netherlands and in sediments along the shallow shore of a deep, large lake, the Spiegelplas in the central area of the Netherlands. I also found it in the river Saar near Saarburg, Germany, in sediments on stones. The species seems to be rare and restricted to clear, mesotrophic waters. However, I found shells in a ditch between meadows, Friesland, the Netherlands, together with Cyphoderia laevis.