Class: Bacillariophyceae

Class: Bacillariophyceae

  • Class: Bacillariophyceae; Dangeard,
  • Scientific name: Bacillariophyceae
  • Domain: Eukaryota
  • Phylum: Ochrophyta
  • Rank: Class
  • Higher classification: Heterokont


  • Diatoms are unicells that share the feature of having a cell wall made of silicon dioxide.
  • This opaline or glass frustule is composed of two parts (valves), which fit together with the help of a cingulum or set of girdle bands.
  • These valves have minute holes that allow the exchange gases, nutrients and wastes with the environment.
  • The Diatoms generally are formed in two general shapes, the centric diatoms, or round, and the pennate diatoms, which are bilaterally symmetrical.
  • These are shown in the pictures at the bottom of the page. On the left is a pennate diatom and on the right a centric.
  • The Diatoms are part of the phytoplankton that are feed on by many marine and freshwater organisms.
  • Their cell wall is not soluble in water so most of them end up on the bottom of lakes and ponds.
  • This sediment will build up and become fossilized rock. This rock is used commercially for everything from abrasives to paper to fertilizer.
  • There are about 10,000 different species of diatoms.
Class: Bacillariophyceae


  • Diatoms are set up with a cell wall made up of silica and the diatom itself is a single-celled photosynthetic protist.
  • These are very little is known about how the cell wall is made, but scientists are researching it to hopefully find a way to reproduce the thin glass-like wall for nanotechnology.
  • Diatoms are autotrophs, which means that they are able to produce their own sugars, lipids and amino acids.
  • During asexual reproduction, the diatom cell size progressively decreases as each valve produces a smaller complementary valve.
  • When the smaller valves have completely formed the two cells must divide; but because one side of the diatom is smaller, when they split one is the same size as the original, while one is smaller yet.
  • When they shrink to a certain size, they have to reproduce sexually. To do this they develop an auxospore which then will become a diatom (see diagram below)
Class: Bacillariophyceae
Cell Cycle


  • Diatoms live in a variety of environments, from salt to fresh water (they are even found in moist soil and mosses), a and a wide range of pH levels, temperatures and organic pollution.
  • This variety of living conditions can help tell pollution or other ecological levels of the water. They also vary in their lifestyle, living singly or in a colony.
  • They do not always float freely in the water, they will attach themselves to a rock or another animal in the water.
  • Diatoms may just seem like they are just part of the plankton that feed that fish and animals.
  • they are huge contributor to the oxygen that is put in to the water and the carbon.
  • It is estimated that 40%, 50 billion to 55 billion tons, of all organic carbon fixation on the planet (transformation of carbon dioxide and water into sugars, using light energy) is carried out by diatoms.
  • This is comparable to all of the world’s tropical rainforests.