Difflugia yorkui Nicholls, 2007
Diagnosis: Shell large, elongated oblong, usually with a distinct neck and covered with large and irregularly shaped siliceous particles except in the anterior region where particles are very small; test roughly circular (not compressed) in transverse cross-section, tapering towards both anterior and posterior ends from its widest point at about the middle of the test. Aperture relatively small and circular, . Organic basal material of the test (cement) organized in an open-meshed pattern of pores 0.3-0.8 µm in diameter separated by ribs 0.2-0.4 µm in width. With zoochlorellae. Nucleus ovular, densely filled with numerous small spherical nucleoli.
Dimensions: Nicholls (2007): Length 305-370 µm; width 140-162 µm; aperture 50-63 µm in diameter (n=12); my measurements: Length 222-460 µm (mean 365 µm); width 118-200 µm; aperture 56-101 µm (n=39).
Ecology: Freshwater; Canada, Netherlands (Naardermeer and several other locations).
Remarks: The identity of the Dutch shells was confirmed by Nicholls (pers. comm., 2021)