Arcella formosa, Ø 204 µm - drawing Ferry Siemensma, 1982
Arcella formosa Nicholls, 2005
Diagnosis: Shell resembling a pie, irregular in outline and with an irregular pattern of rib-like structures and depressions; ribs often darker than the rest of the shell. Multinucleated, up to 25 nuclei.
Dimensions: Nicholls: diameter 135-265 µm; my measurements: diameter 114-345 µm. Tests of the population of the Bert Bospad varied in size between 114 and 230 µm!
Ecology: Freshwater; in sediment of mesotrophic ditches. Rare. I found this species in 't Hol, the Bert Bospad and around the Naardermeer, all in the Netherlands. Nicholls described it from Canada.
Remarks: This species was first recognized by Siemensma, 1982, who only published a drawing with the name Arcella robusta. Later this species was also found by Nicholls in Canada and formally described by him as Arcella formosa.
Arcella formosa, 258 µm - Bert Bospad, stacked image. Shells can look distorted, but this is a normal shape.
Arcella formosa, 162 µm - living cell with one nucleus arrowed. Note the variety of food particles, e.g. green algae and purple bacteria
Arcella formosa, 241 and 121 µm - Bert Bospad
Arcella formosa, small and large specimen, both from the same sample (114 and 235 µm - Bert Bospad)
Arcella formosa, 211 µm - Bert Bospad, stacked image
Arcella formosa, 147 and 160 µm - Bert Bospad
Arcella formosa, 165 and 180 µm - Bert Bospad
Arcella formosa, 257 and 172 µm, Bert Bospad
Arcella formosa, 177 and 124 µm, Bert Bospad
Arcella formosa, 184 and 185 µm, Bert Bospad
Arcella formosa, 132 µm - detritus Naardermeer
Arcella formosa, 132 um side view - stacked image
Arcella formosa, (l.) 190 µm, Kromme Rade, 2014 and (r.) 177 µm, Bert Bospad, 2016.
My first drawings of Arcella formosa, 1979
Arcella formosa, 170 µm - Naardermeer, 2012