Netzelia corona (Wallich, 1864) Gooma et al., 2017
Syn.: Protocucurbitella coroniformis Gauthier-Lièvre & Thomas, 1960
Diagnosis: shell spherical to sub-spherical. The shell wall is composed of mineral grains, quartz and diatom frustules, which are agglutinated together by an organic cement. The shell is ornamented by conical hollow spines at the posterior third. The aperture is circular, surrounded by a variable number of inward-oriented angular crenulations (tooth-like structures). Shells ornated with tuberculate structures similar to Netzelia tuberculata have been observed by Vucetich (1973) and Siemensma (2013, see https://www.arcella.nl/difflugia-corona,https://www.arcella.nl/difflugia-urceolata).
Dimensions: 140-320 µm (Leidy); 200-250 µm (Penard); 180-310 µm (Awerinzew); 180-230 µm (Cash); 155-200 µm(Hoogenraad & De Groot); 80-380 µm (Lahr & Lopes); my measurements 105-193 µm, mean 156 µm.
Ecology: Fresh water, in different water types; in sediments, in sphagnum, on waterplants, often very common. This species has been found in icefield lakes high in the mountains (Monti 1906).
Remarks: Sometimes the shell has a tuberculate structure as in D. tuberculata. The number of conical spines I counted in Dutch specimen is commonly 4-6.