Compare

Pinnularia formica has a much more exaggerated triundulate outline, with a more prominently expanded central margin.

LM scalebar = 10 µm
Pinnularia polyonca LM5 Pinnularia polyonca LM4 Pinnularia polyonca LM3 Pinnularia polyonca LM2 Pinnularia polyonca LM1
Length Range
68-80 µm
Width Range
8.9-10.3 µm
Striae in 10 µm
10-12

Also compare to

Pinnularia formica

(Ehrenb.) R.M.Patrick 1966