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.
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