Hantzschia amphioxys (Ehrenberg) Grunow (Figs 75–93)

Basionym: Eunotia amphioxys (Ehrenberg1843: 413) Grunow (in Cleve & Grunow 1880: 103)

Morphology of the observed population: Valves clearly dorsiventral with convex ventral side. Dorsal side distinctly concave in middle, but convex near the apices. Valve apices clearly protracted and sub-capitate. Valve dimensions (n=30): length 23.5–69.5 μm, width 4.5–5.8 μm. Width at widest part of the valve face: 4.6–5.9 μm. Unequally spaced fibulae, 5–11 in 10 μm. Each fibulae connected to 1–4 transapically costae (Figs 89, 92). Striae in middle part of the valve slightly radiate, becoming parallel toward the apices, 23–29 in 10 μm. Areolae not discernible in light microscope (45–50 in 10 μm). Distal raphe endings clearly hooked. Internally, fibulae not equidistant. Central raphe endings deflected to opposite directions.

Taxonomic remarks: The observed population (Sample No. 2018/436) was characterized by longer valves comparing with other populations from the literature data (Tab. 2). Nevertheless other features including valve width, striae and areolae density as well as internal and external proximal raphe endings confirm compliance with the current morphological concept of this species.