Diatoms in General:
Diatoms are Eukaryotic cells which can be found anywhere where photosynthesis is possible, intern they can be found in most places around the world. While they can come in a multitude of shapes and sizes, all of them fit under the order Bacillariophyceae (Pennate) or Coscinodiscophyceae (Centric). Of course, no matter their form their physiology remains semi-consistent. They all have shells made of a glass-like substance called silica. This shell has two valves and is clear allowing for light to reach the chloroplasts inside. They are the same color as their chloroplasts and can even have a golden tint based on the concentration of fucoxanthin and carotene. They can between 2 to 500 microns, which is about the width of a human hair. Despite their size they supply about 20% -40% of the oxygen to Earth making them essential to the oxygen cycle. Overall, due to their importance to the ecosystem and their prevalence in the world they are ideal for comparing streams.
The Two Orders:
Bacillariophyceae (Pennate)
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Pennates are one of the two orders of diatoms, and despite their many similarities there are a number of differences between them. Pennales have elongated valves giving them a more ovular shape. In terms of habitat association they are able to move freely through the use of Cilia and can be found in both salt and freshwater environments.
Coscinodiscophyceae (Centric)
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Centric diatoms are the other order they can be born into. Unlike Pennales, Centrales hold a rounder shape. Despite this, they appear rectangular when in a colony. Typically these colonies are attached to rocks and can reach lengths between 20 to 200 microns.
After Death
Diatomite, or diatomaceous earth, is the generated during aftermath of a diatom death. Once diatoms die their silica shells stay behind and build up into the hardened substance. It is often sought after for its absorptive, abrasiveness, insulative, and high silica contents.
