Arcella formosa
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: my measurements: 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.

 

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 and formally described as Arcella formosa.

 

Arcella robusta formosa
Arcella formosa, 258 µm - Bert Bospad, stacked image. Shells can look distorted, but this is a normal shape.
Arcella robusta formosa
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 robusta formosa
Arcella formosa, small and large specimen, both from the same sample (114 and 235 µm - Bert Bospad)
Arcella robusta formosa
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 robusta formosa
Arcella formosa, 132 µm - detritus Naardermeer
Arcella robusta formosa
Arcella formosa, 132 um side view - stacked image
Arcella formosa, (l.) 190 µm, Kromme Rade, 2014 and (r.) 177 µm, Bert Bospad, 2016.
Arcella formosa robusta
My first drawings of Arcella formosa, 1979
 
Arcella formosa
Arcella formosa, 170 µm - Naardermeer, 2012