Diatoms (Greek: dia = through + temnein = to cut: "cut through") are a big group of eukaryotic algae. They are one of the most common types of phytoplankton. Most diatoms are unicellular, although some form chains or simple colonies. Diatom cells are encased within a unique cell wall made of silica (SiO2). These walls, called frustules, take many forms, some quite beautiful and ornate. They usually consist of two asymmetrical sides with a split between them, which gives the group its name.
Diatom chloroplasts were probably derived from those of red algae. The fossil record of diatoms starts in strata of the Lower Jurassic, ~185 million years ago. Molecular clock evidence suggests an earlier date for their origin. The entire genomes of two species of diatom have been analysed. The analysis reveals that hundreds of genes in both species came from bacteria.
Diatoms have some practical uses. Diatom communities are a popular tool for monitoring environmental conditions, past and present. They are commonly used in studies of water quality. They are also of interest to nanotechnology.
Images for kids
Diatomaceous earth as viewed under bright field illumination on a light microscope. Diatomaceous earth is a soft, siliceous, sedimentary rock made up of the cell walls of diatoms and readily crumbles to a fine powder. This sample consists of a mixture of centric (radially symmetric) and pennate (bilaterally symmetric) diatoms. This image of diatomaceous earth particles in water is at a scale of 6.236 pixels/μm, the entire image covers a region of approximately 1.13 by 0.69 mm.
Selections from Ernst Haeckel's 1904 Kunstformen der Natur (Art Forms of Nature), showing pennate (left) and centric (right) frustules.
Diatom Facts for Kids. Kiddle Encyclopedia.