Chaetoceros socialis (Bacillariophyta, Coscinodiscophyceae, Chaetocerotales, Chaetocerotaceae), diameter of colony 460 µm, Sylt 9. 2015. 0:58 min. Chaetoceros is a genus with more than 400 species inside the Bacillaryophyta, which form chains of cells, called frustules, equipped with two or more long and thin setae. Frustules form long chains. In Chaetoceros socialis frustules are comparatively small (large diameter 2-15 µm, small diameter 2-10 µm) and the short chains are embedded in in a gelatinous mass, reaching more than 1 mm in diameter. Video can be used for teaching.