Diatom

Diatoms are a group of eukaryotic microalgae within the class Bacillariophyceae, comprising unicellular or colonial organisms that perform photosynthesis. They are notable for their silica-based cell walls, called frustules, which consist of two interlocking halves and display intricate, species-specific patterns.

Frustules come in two major shapes: centric and pennate. Diatoms range in size from about 2 to 200 micrometers. They contain pigments such as chlorophyll a and c and fucoxanthin, giving them a brownish hue.

Ecology and distribution: They occur in virtually all aquatic environments, from open oceans to freshwater lakes and damp soils, and form a substantial portion of phytoplankton. Through photosynthesis they contribute a significant share of global primary production and carbon fixation, helping drive the marine silica cycle, as they extract dissolved silica from water to build their frustules.

Life cycle and reproduction: Most diatoms reproduce asexually by cell division, which gradually reduces the size of the population; sexual reproduction eventually restores cell size and restarts the cycle via auxospore formation.

Human relevance: Diatomaceous earth, composed of fossil diatom frustules, is used as filtration aids, polishing agents, absorbents, and insecticides. Diatoms serve as important bioindicators for water quality, and in some taxa, such as Pseudo-nitzschia, can produce toxins during harmful algal blooms. The fossil record provides valuable information for paleoclimate studies.