Rabdiophrys monopora (Thomsen, 1978) Roijackers and Siemensma, 1988
Diagnosis: Scales of two types. Protoplast unknown. Plate-scales circular, c. 2.5 µm in diameter, with one big central hole through the distal scale surface. Between a patternless scale rim and the central hole is an area perforated by hexagonally packed minute holes. The lower scale-plate – visible through the central hole – is likewise perforated by small holes arranged in a distinct hexagonal pattern. The two scale-plates are fused peripherally, elsewhere interconnected by material which appears in places as hexagonally arranged black dots.
Spine-scales c. 1.5 µm long and 0.7 µm broad at the base, flattened distally into a bifurcate tip, proximally attached by extensions from the two decurrent ridges to an oval base-plate. Occasionally a large hole is present just above the base of the spine-scale.
Type location: Freshwater (5 °C). Appeared in a three weeks old raw culture set up from a surface water sample collected from lake Esrom (Denmark).
Remarks: I have found many plate-scales of this species in a wide variety of mainly eutrophic freshwater bodies all over the Netherlands.