Differential interference contrast (DIC) light micrograph of the freshwater diatom Asterionella formosa. Asterionella belongs to the pennate diatoms (penna: Latin for feather). Asterionella forms star-shaped colonies in order to be able to float better planktically in the water column. The single cells contain wall-bound chloroplasts whose brown colour is caused by the dye fucoxanthin. Here the cell is seen in shell view. Magnification: x800 at a print width of 10 centimetres.