Light micrograph of Thalassiosira sp. (Gr. thalassa, sea & Gr. seira, chain) marine diatom colony. Thalassiosira occurs as cells in chains linked by chitin threads. Sample taken from the North sea in the Nederlands. 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.