Lithodesmium undulatum (Bacillariophyta, Coscinodicophyceae, Leptocylindrales, Leptocylindraceae), cell diameter 52 µm, Sylt 10.2015. 1:02 min. Cells rectangular in girdle view and triangular in valve view. Cells are connected by the so-called marginal riches and a central bilabiate process thus forming straight chains including large gaps between cells. Many chloroplasts in often X-formed arrangement. Video can be used for teaching.