Rabdiophrys anulifera Rainer, 1968, emend. Siemensma, 1981
Diagnosis: Cells 27-35 µm in diameter, covered with plate- and spine-scales. The species resembles much R. monopora, and differs from it in having small (1.2-3.4 µm) as well as long spine-scales (10-12.2 µm) and an aberrant ultrastructure of the plate-scales. Both species have plate-scales consisting of 2 layers fused peripherally and in the case of R. anulifera by 2 concentric internal rims, one lying halfway between the periphery and the central hole and the other rim just around the border of the central hole. These rims can sometimes be seen by SEM. In R. monopora the 2 layers of the plate-scales are also fused peripherally, but they are interconnected by material which appears in places as black dots, as could be seen by TEM. The diameter of the plate-scales of R. anulifera is 2.1-2.8 µm with the central hole ca. 0.8 µm in diameter. The spine-scales are distally strongly flattened and somewhat broadened, ornamented with 2 small and pointed teeth. The shaft is 0.24-0.50 µm in diameter; the apex is ca. 0.7 µm broad. Proximally the shaft is connected to a circular base plate, 0.57-1.2 µm in diameter, by four wing-like structures.
Remarks: This species was studied with transmission electron microscopy by Nicholls (1983) and described as P. pinea, now a junior synonym of R. anulifera. This species has been reported from Germany (Rainer 1968), The Netherlands (Siemensma 1981) and Canada (Nicholls 1983), all from freshwater localities. I found this species again in 2011, 2015 and 2019 at several locations in the Netherlands.