Gyrosigma is a genus of diatoms belonging to the family Pleurosigmataceae.

The genus has a cosmopolitan distribution.

Like other diatoms, Gyrosigma has a siliceous cell wall called a frustule. The frustule is composed of two sections called valves, with one valve fitting inside the other valve similar to the two halves of a Petri dish. Gyrosigma has valves with a central slit called a raphe, a structure that allows movement of these diatoms.

The valves of Gyrosigma are sigmoid in outline, as well as the raphe. Striations could be parallel or perpendicular to the raphe. This contrasts to a similar genus Pleurosigma, which has striations that lie diagonally to the raphe.

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