The unique feature of diatoms are that they are surrounded by a cell wall made of silica (hydrated silicon dioxide), called a frustule. Diatoms have two distinct shapes: a few ( centric diatoms) are radially symmetric, while most ( pennate diatoms) are broadly bilaterally symmetric.

In the presence of adequate nutrients and sunlight, an assemblage of living diatoms doubles approximately every 24 hours by asexual multiple fission the maximum life span of individual cells is about six days. Individual cells range in size from 2 to 200 micrometers. ĭiatoms are unicellular organisms: they occur either as solitary cells or in colonies, which can take the shape of ribbons, fans, zigzags, or stars. The shells of dead diatoms can reach as much as a half-mile (800 m) deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion tonnes of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. Bacillariophyta Engler & Gilg, 1919 Ī diatom ( Neo-Latin diatoma) is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world.Light microscopy of a sampling of marine diatoms found living between crystals of annual sea ice in Antarctica, showing a multiplicity of sizes and shapes

Detailed scum map