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Gyrosigma attenuatum is similar in shape but valves are much larger and the striae are more coarse. In addition, the longitudinal striae are more distinct than the transverse striae. The proximal raphe ends of G. rautenbachiae extend farther toward the valve margin and cross the first row of longitudinal striae. Gyrosigma spencerii is considered synonymous with G. acuminatum.

LM scalebar = 10 µm
Images 3 Images 4 Images 5 Images 1 Images 2
Length Range
77-153 µm
Width Range
11-18 µm
Striae in 10 µm
transverse 18-20; longitudinal 18-22

Gyrosigma attenuatum

(Kütz.) Rabenh. 1853

Gyrosigma attenuatum LM4 Gyrosigma attenuatum LM10 Gyrosigma attenuatum LM14 Gyrosigma attenuatum LM8 Gyrosigma attenuatum LM2 Gyrosigma attenuatum LM6 Gyrosigma attenuatum LM12
Length Range
130-255 µm
Width Range
20-28 µm
Striae in 10 µm
12-14 transverse; 10-12 longitudinal

Also compare to

Gyrosigma rautenbachiae

Cholnoky