Differential interference contrast (DIC) light micrograph of the marine diatom Gyrosigma fasicola. Gyrosigma belongs to the pennate diatoms (penna: Latin for feather). The single cells contain wall-bound chloroplasts whose brown colour is caused by the dye fucoxanthin. Here the cell is seen in shell view. The focus is on the centre of the cell with the nucleus in the middle of the shell. Magnification: x600 at a print width of 10 centimetres.