Differential interference contrast light micrograph of Ditylum brightwellii, a marine diatom, found in the North Sea. Ditylium brightwellii has a worldwide distribution in boreal to tropical coastal and estuarine environments, apparently absent only from polar oceans. Diatoms are an important part of the phytoplankton in the cold oceans. Magnification: 380x when printed at 10 centimetres wide.