Having the shape of a wave, with crests and troughs. A valve may be undulate on the margins or on the face.
Image Credit: Sarah Spaulding, Elizabeth Ruck
Light micrographs of Cymatopleura. On the left, a frustule in girdle view shows the undulations characteristic of the genus. On the right, the undulations are visible in valve view.
Image Credit: Megan Otu
Chamaepinnularia soehrensis is a small diatom (scale bar = 10 µm) with an undulate valve margin.