There are two types of plankton: tiny plants--called phytoplankton, and weak-swimming animals--called zooplankton. Some are babies that will grow into strong-swimming, non-planktonic adults. Others will remain plankton for their entire lives. They are single-celled yellow algae whose cell walls contain a lot of silica, glass-like substance. The actual diatom fits inside this cell wall, with one half of the wall fitting over the second half, like a lid. The name diatom actually means cut in two in Greek. Silicate is used by diatoms in the formation of their frustules (a glass-like “shell” in which the diatom lives), and it is true that in some cases addition of silicate to an aquarium can result in diatoms getting a competitive edge over other algae. That is the reason that you are likely to see diatoms on primarily or only the walls of your glass aquarium – diatoms have a much easier time pulling silicate out of glass aquarium walls than out of quartz sand grains. Nearly all diatoms are microscopic-cells range in size from about 2 microns to about 500 microns (0.5 mm), or about the width of a human hair (note that one micron is equal to 10 -6 meter). Diatoms grow as single cells or form filaments and simple colonies. Ecology. Diatoms are abundant in nearly every habitat where water is found – oceans, lakes, streams, mosses, soils, even the bark of trees. These algae form part of the base of aquatic food webs in marine and freshwater habitats. Basically, diatoms live in glass boxes. The silica shell of the diatom is called the 'frustule' and is made of two halves, each in turn composed of several different pieces. 1 Centric diatoms of this kind are often referred to as 'polar centrics'. 2  the polar centrics rarely appear in molecular phylogenies as a monophyletic group; instead, they are usually paraphyletic with respect to the pennate diatoms. Phytoplankton. Diatoms are the most common type of phytoplankton. They are single-celled yellow algae whose cell walls contain a lot of silica, glass-like substance. The actual diatom fits inside this cell wall, with one half of the wall fitting over the second half, like a lid. The name diatom actually means cut in two in Greek. Diatoms are algae with distinctive, transparent cell walls made of silicon dioxide hydrated with a small amount of water (Si02 + H20). Silica is the main component of glass and hydrated silica is very like the mineral opal, making these algae, often called algae in glass houses more like algae in opal houses. The cell wall is called a frustule and consists of two halves called valves. Since silica is impervious, diatoms have evolved elaborate patterns of perforations in their valves to allow nutrient and waste exchange with the environment. Diatoms grow as single cells or form filaments and simple colonies. Ecology. Diatoms are abundant in nearly every habitat where water is found – oceans, lakes, streams, mosses, soils, even the bark of trees. These algae form part of the base of aquatic food webs in marine and freshwater habitats. Diatoms are a major group of algae, and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons (e.g. Fragilaria), fans (e.g. Meridion), zigzags (e.g. Tabellaria), or stars (e.g. Asterionella). A unique feature of diatom cells is that they are enclosed within a cell wall made of silica (hydrated silicon dioxide) called a frustule. These frustules show a wide diversity in form, but are usually almost bilaterally symmetrical, hence the group name Diatoms are one of the most common types of phytoplankton and a major group of algae. They constitute a large percentage of all living matter in oceans, rivers and lakes. One species, Didymosphenia geminata, is responsible for creating thick blooms in mountain streams and ponds.  John. Rob, Like many other people, I have pretty fast diatom growth on the glass of my aquarium, and have to scrape a lot. I have seen a number of solutions proposed by various people about controlling diatom growth in tanks, and the general consensus is that diatoms are regulated by silicon in the tank water. That is the reason that you are likely to see diatoms on primarily or only the walls of your glass aquarium – diatoms have a much easier time pulling silicate out of glass aquarium walls than out of quartz sand grains.
http://www.whoi.edu/science/B/people/kamaral/plankton.html http://saltcorner.com/Articles/Showarticle.php?articleID=63 http://westerndiatoms.colorado.edu/about/what_are_diatoms http://tolweb.org/Diatoms/21810 http://www.whoi.edu/science/B/people/kamaral/plankton.html http://westerndiatoms.colorado.edu/about/what_are_diatoms https://en.wikipedia.org/wiki/Diatom http://www.livescience.com/28690-ranger-tacc-diatoms-research-nsf-bts.html http://saltcorner.com/Articles/Showarticle.php?articleID=63
things commonly mistaken for diatoms