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Note that a broad concept is presented here. See text to left for further explanation. This broad concept species is sometimes confused with Nitzschia amphibia, which is often found in the same habitats as N. semirobusta and is of similar size and shape. However, N. amphibia lacks the thickened fibulae that are characteristic of N. semirobusta. Furthermore, N. amphibia has a prominent central nodule which N. semirobusta lacks.

Nitzschia semirobusta may also be confused with Denticula kuetzingii. The fibulae of D. kuetzingii, however, completely extend across a valve from margin to margin with a similar thickness, while the fibulae of N. semirobusta decrease in thickness as they extend across the valve from margin to margin.

LM scalebar = 10 µm
Nitzschia semirobusta LM4 Nitzschia semirobusta LM3 Nitzschia semirobusta LM2 Nitzschia semirobusta LM1 Nitzschia semirobusta LM5
Length Range
9.5-22 µm
Width Range
4.3-5.2 µm
Striae in 10 µm
14-18

Nitzschia amphibia

Grunow 1862

Nitzschia amphibia LM3 Nitzschia amphibia LM5 Nitzschia amphibia LM2 Nitzschia amphibia LM1 Nitzschia amphibia LM4
Length Range
14-37 µm
Width Range
4.0-4.5 µm
Striae in 10 µm
14-18

Also compare to

Denticula kuetzingii

Grunow