Diatom alga. Light micrograph of Navicula lyra, a diatom alga. The Navicula genus is found in the surface layers of damp soil, producing food from sunlight by photosynthesis. Diatoms are single- celled algae which produce an intricately patterned, glass-like cell wall, or frustule. The frustule consists of two halves which fit together like the lid and bottom of a box. It is often decorated with rows of tiny holes, known as striae. There are about 10,000 species of diatom algae in freshwater and marine habitats. Magnification: x160 at 35mm size.