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Aulacoseira granulata var. angustissima differs from A. granulata by having a combination of long and narrow valves with diameter of 2.5-4 μm and mantle height/valve diameter ratio greater than 3.2. Specimens with either valve diameter greater than 4 µm, or mantle height/valve diameter ratio lower than 3.2, or both, should be placed in A. granulata. Specimens of A. granulata var. angustissima with fine areolae can be confused with A. ambigua, which is recognizable by its hollow ringleiste and absence of long separation spines.

LM scalebar = 10 µm
Aulacoseria granulata var. angustissima LM1 Aulacoseria granulata var. angustissima LM2 Aulacoseria granulata var. angustissima LM7 Aulacoseria granulata var. angustissima LM6 Aulacoseria granulata var. angustissima LM3 Aulacoseria granulata var. angustissima LM4 Aulacoseria granulata var. angustissima LM5
Diameter
2.5-4 µm
Width Range
8-20 µm
Striae in 10 µm
10-20

Aulacoseira ambigua

(Grunow) Simonsen 1979

Aulacoseira ambigua LM5 Aulacoseira ambigua LM6 Aulacoseira ambigua LM3 Aulacoseira ambigua LM4 Aulacoseira ambigua LM7 Aulacoseira ambigua LM1 Aulacoseira ambigua LM2
Diameter
3-12 µm
Width Range
5-15 µm
Striae in 10 µm
17-22

Aulacoseira granulata

(Ehrenb.) Simonsen 1979

Aulacoseira granulata LM1 Aulacoseira granulata LM2 Aulacoseira granulata LM3 Aulacoseira granulata LM4 Aulacoseira granulata LM5 Aulacoseira granulata LM6
Diameter
4-17 µm
Width Range
4-20 µm
Striae in 10 µm
8-18