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Brachysira brebissonii has smaller, more lanceolate valves with a higher density of striae (26-35 in 10 µm).

LM scalebar = 10 µm
Brachysira arctoborealis LM1 Brachysira arctoborealis LM2 Brachysira arctoborealis LM3 Brachysira arctoborealis LM4 Brachysira arctoborealis LM5 Brachysira arctoborealis LM6
Length Range
21.7-48.2 µm
Width Range
7.2-12.1 µm
Striae in 10 µm
24-26

Brachysira brebissonii

R.Ross in B.Hartley 1986

Brachysira brebissonii LM7 Brachysira brebissonii LM6 Brachysira brebissonii LM5 Brachysira brebissonii LM4 Brachysira brebissonii LM3 Brachysira brebissonii LM2 Brachysira brebissonii LM1
Length Range
11-36 µm
Width Range
4-8 µm
Striae in 10 µm
26-35