A diatom is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. 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. The shells of dead diatoms can reach as much as a half-mile 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.
Trichodesmium, also called sea sawdust, is a genus of filamentous cyanobacteria. They are found in nutrient poor tropical and subtropical ocean waters. Trichodesmium is a diazotroph; that is, it fixes atmospheric nitrogen into ammonium, a nutrient used by other organisms. Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally. Trichodesmium is the only known diazotroph able to fix nitrogen in daylight under aerobic conditions without the use of heterocysts.
Micrasterias is a unicellular green alga of the order Desmidiales. Its species vary in size reaching up to hundreds of microns.
Chaetoceros is a genus of diatoms in the family Chaetocerotaceae, first described by the German naturalist C. G. Ehrenberg in 1844. Species of this genus are mostly found in marine habitats, but a few species exist in freshwater. It is arguably the common and most diverse genus of marine planktonic diatoms, with over 200 accepted species. It is the type genus of its family.
Bacillariaceae is a family of diatoms, the only family in the order Bacillariales. Some species of genera such as Nitzchia are found in halophilic environments; for example, in the seasonally flooded Makgadikgadi Pans in Botswana.
Amphora is a major genus of marine and freshwater diatoms. With over 1000 species, it is one of the largest genera of diatoms. These diatoms are recognized by their strongly dorsiventral frustules, which means that their ridges lie close to the ventral margin of the valve, and their girdle is much wider on the dorsal side.
Eunotiaceae is a family of diatoms in the order Eunotiales that includes the following genera:
Luticola is a genus of marine diatoms.
Cyclotella is a genus of diatoms often found in oligotrophic environments, both marine and fresh water. It is in the family Stephanodiscaceae and the order Thalassiosirales. The genus was first discovered in the mid-1800s and since then has become an umbrella genus for over 100 different species, the most well-studied and the best known being Cyclotella meneghiniana. Despite being among the most dominant genera in low-productivity environments, it is relatively understudied.
Adlafia is a genus of diatoms belonging to the family Anomoeoneidaceae.
Cosmioneis is a genus of diatoms belonging to the family Cosmioneidaceae.
Diploneis is a genus of diatoms belonging to the family Diploneidaceae.
Gomphonema is a genus of diatoms belonging to the family Gomphonemataceae.
Mastogloia is a genus of diatoms belonging to the family Mastogloiaceae. The genus has cosmopolitan distribution, primarily in marine waters.
Melosira is a genus of diatoms belonging to the family Melosiraceae.
Stauroneis is a genus of diatoms (Bacillariophyta) with species that occur in fresh and marine water.
Nupela is a genus of diatom. Species of Nupela typically measure less than 20 μm. The genus was first described as being isovalvar, however many recently described species are heterovalvar. The main diagnostic characteristic of the genus is the presence of an external covering over the areolae. The genus was circumscribed by Wim Vyverman and Pierre Compère in 1991, with Nupela giluwensis assigned as the type, and at that time, only species.
