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. Microscopic contrast method : Differential interference contrast. Magnification 380x when printed at 10 centimetres wide.