Arcella mitrata  Leidy, 1876

Diagnosis: Shell balloon-shaped or polyhedral; height more or less the same as the diameter of the base; aperture circular, crenelated and usually averted within inverted funnel; protoplasmic body spheroidal, with ‘neck’ to aperture and cytoplasmic strands to test; six or more slender lobopodia.

Dimensions: Shell diameter 100—180 µm; height 100—162 µm. My measurements: Diameter 119—218 µm (mean 144 µm); height 80—200 µm (mean 139 µm).

Ecology: Freshwater, in submerged Sphagnum and Utricularia. Rare.

Dutch locations: Baarn (Groeneveld); Hilversum (Bluk); Harskamp (Loofles); Dwingeloo (Diepveen); Fochteloërveen; Haaksbergerveen; Nunspeet (fen); Huizen (fen); Eindhoven (Strabrechtse heide, Wim van Egmond).

Remarks: I have found this species in oligothrophic and mesotrophic shallow ponds, the bottom covered with sand and/or Sphagnum. Earlier reports for the Netherlands were given by Hoogenraad and De Groot, 1940.