Light micrograph of Melosira sp. (Greek melon, apple and Greek seira, chain) diatoms. Melosira occurs as chain of cylindrical cells joined valve to valve. Diatoms are an important part of the phytoplankton in the cold oceans and freshwater habitats as well. Microscopic contrast method : Differential interference contrast. Magnification 680x when printed at 10 centimetres wide.