Differential interference contrast light microscopy of Peridinium sp. dinoflagellates from a small moor puddle. This unicellular freshwater organism is covered by two thick thecal plates and is therefore known as an armoured dinoflagellate. Each cell also has two flagella (hair-like structures) that are used for locomotion. Population explosions of Peridinium sp. dinoflagellates can form brown blooms that are similar to red tides. Captured field width: 0.26 millimetres.