A diatom frustule
"Colour-enhanced image of a diatom frustule. The frustule is the silicon cell wall that acts as a skeleton to support the single-celled diatom. In this image only the frustule and none of the cell contents remain. Diatoms have chloroplasts and can use sunlight to produce food. They are a major component of plankton in both fresh and salt water."

Diatoms | jecesq

Coloured scanning electron micrograph (SEM) of assorted diatoms. The diatoms are a group of photosynthetic, single-celled algae containing about 10,000 species. They form an important part of the plankton at the base of the marine and freshwater food chains. The characteristic feature of diatoms is their intricately patterned, glass-like cell wall, or frustule. The frustule often has rows of tiny holes, known as striae.