diatome

A diatome, or diatom, is a photosynthetic microalga belonging to the group Bacillariophyta, within the larger heterokont lineage of the Stramenopiles. Diatoms are unicellular or occur in simple colonies and are among the most diverse and abundant phytoplankton groups in aquatic ecosystems.

Diatoms are characterized by their unique cell wall, called a frustule, made of hydrated silica (opaline silica). The frustule consists of two halves, a larger epitheca and a smaller hypotheca, that fit together. The sculptured patterns on the frustule provide mechanical protection and may influence buoyancy and light capture.

Ecology: They inhabit freshwater and marine environments, from rivers to the open ocean; certain species also occur in moist soils. They are primary producers and contribute significantly to global photosynthesis and carbon fixation. They require dissolved silica for frustule formation. Reproduction is mainly asexual with gradual size reduction, followed by sexual reproduction to restore cell size and genetic diversity.

Fossils and uses: Diatom frustules persist as excellent microfossils, forming deposits of diatomaceous earth. This material is used for filtration, as an abrasive, and in various biotechnological applications. The silica shells also provide valuable records of past climates and nutrient conditions.

Taxonomy and species: There are thousands of species with diverse forms, including centric diatoms with radial symmetry and pennate diatoms with bilateral symmetry. Taxonomic relationships are refined with molecular data. Diatoms are a key component of aquatic food webs and serve as important bioindicators of environmental change.