Formally known as Bacillariophyta, diatoms are unicellular microalgae with a silicon-based cell wall found mostly in marine and freshwater environments. The global diversity of diatoms is estimated to be around 10 000 species and they are mostly photosynthetic and are therefore a primary food source in many aquatic environments. They can either be found floating in the water column as plankton or attached to a substrate and large deposits of dead diatoms in the sediment can produce what is known as diatomaceous earth with huge mineral deposits rich in silica.

Diatoms have a unique structure in that they have a porous silica cell wall that is split into two halves called frustules. A large upper frustule sits on top of and encloses a smaller lower frustule. The two distinct shapes of a diatom split the Bacillariophyta into two separate classes: the pinnate and centric diatoms. The pinnate diatoms are long and thin, shaped like a needle or boat whereas centric diatoms have circular wheel-shaped frustules.

Reproduction mostly occurs by one diatom splitting in half and each half producing another frustule to produce two complete diatoms. The newly produced frustule is always smaller than the original frustule and so each generation is smaller than the previous. When a diatom is too small to reproduce through this asexual method they alter their method of reproduction to reproduce sexually.

Last edited: 25 May 2015

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