Solitary cell, circular in shape. Generally settles in valve view. The edge of the cell is distinct, hyaline and can be finely striated. On the valve surface are areolae arranged in clusters, while the marginal area often has densely-packed areolae and/or striae in pointing in different directions.

At the centre of the valve is the annulus which differs from species to species in terms of size and visibility. There is also a pseudonodule, which also varies from species to species in terms of size and visibility. There are no labiate processes at the centre of the valve, but they are present on the margin and arranged in a ring.

In the cytoplasm there are numerous discoid chloroplasts.