Guide to Gyrosigma

Valves are sigmoid. The axial area is narrow and also sigmoid, containing a sigmoid raphe. The striae are comprised of punctate areolae and form rows that are perpendicular and parallel to the apical and transapical axes. The central area is round to elliptic. External proximal raphe ends are deflected in opposite directions from one another. In living cells, two plastids are present.

Gyrosigma is characteristic of epipelic and endopelic habitats. The genus is widely distributed in freshwaters, with some species found in brackish waters.