Euplotes protozoan and diatoms. Coloured scanning electron micrograph (SEM) of Euplotes sp. hypotrich ciliate protozoa and diatoms. Euplotes and other protozoans in the same genus have rows of fused cilia called cirri along their ventral side. The cirri are used for swimming and walking. Diatoms are planktonic unicellular algae. They have a mineralised cell wall (frustule) divided into two halves. The frustule contains silica and provides protection and support. Magnification: x800 when printed 10 centimetres wide.