Diatom


 * Latin Name-** Achnanthes Angustota
 * Kingdom-** Protista
 * Phylum-** Heterokontophyta


 * __Description:__** Most diatoms are unicellular ,although they can exist as colonies in the shape of filaments or ribbons (e.g. //Fragillaria//), fans (e.g. //Meridion//), zigzags or stellate colonies. Diatoms are producers within the food chain. A characteristic feature of diatom cells is that they are encased within a unique cell wall made of silica (hydrated silicon dioxide) called a frustule. Diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality.


 * __Features:__** They are especially important in oceans, where they are estimated to contribute up to 45% of the total oceanic primary production. Spatial distribution of marine phytoplankton species is restricted both horizontally and vertically. Diatoms occur in all oceans from the poles to the tropics; polar and subpolar regions contain relatively few species compared with temperate biota. Although tropical regions exhibit the greatest number of species, more abundant populations are found in polar to temperate regions. Usually mircroscopic, some species of diatoms can reach up to 2mm in length. Diatom frustules are composed of very pure hydrated silica within a layer of organic, carbon containing material. Frustules are really comprised of two parts: an upper and lower frustule. The larger upper portion of the frustule is called the epitheca. The smaller lower piece is the hypotheca. Diatom cells within frustules contain chloroplasts, the organelles in which photosynthesis occurs. Chloroplasts contain chlorophyll, the pigment molecule that allows plants and other photosynthetic organisms to capture solar energy and convert it into usable chemical energy in the form of simple sugars.


 * __Habitat:__** First recorded occurrences of diatoms are from the Jurassic, however, these are uncertain and the earliest recorded well preserved diatoms are centric forms from the Aptian-Albian stages of the Cretaceous. The earliest freshwater diatoms appear in the Palaeocene in Russia and the Late Eocene in North America. As with coccoliths, the earliest forms in the fossil record may reflect a biomineralisation event rather than an evolutionary appearance. The earliest araphid diatoms appear in the Late Cretaceous, and raphid pennates in the Middle Eocene.


 * __More Facts:__** Diatom frustules found in sedimentary rock are microfossils. Because they are so easily preserved, diatoms have an extensive fossil record. Specimens of diatom algae extend back to the Cretaceous Period, over 135 million years ago. Some kinds of rock are formed nearly entirely of fossilized diatom frustules. Considering the fact that they are microscopic organisms, the sheer numbers of diatoms required to produce rock of any thickness is staggering. Rock that has rich concentrations of diatom fossils is known as diatomaceous earth, or diatomite. Diatomaceous earth, existing today as large deposits of chalky white material, is mined for commercial use in abrasives and in filters. The fine abrasive quality of diatomite is useful in cleansers, like bathtub scrubbing powder. Also, many toothpaste products contain fossil diatoms.

__**Resources:**__ Round, F. E., et al. //Diatoms: Biology and Morphology of the// //Genera.// Cambridge University Press, 1990. Stoermer, Eugene F., and John P. Smol. //The Diatoms: Applications for the Environmental and Earth Sciences// Cambridge University Press, 1999. [] []