Last month I found these Arcella shells in the Diepveen, an old moor fen in the Netherlands. The large shell is Arcella mitrata, 130 µm high. The smaller one, 85 µm high, was described by Deflandre in 1928 as A. mitrata var. spectabilis. I found the differences between both type of shells so significant, that I'm convinced that the latter is a separate species and should be named A. spectabilis.

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