What are diatoms?

(Project Update: Diatoms & Desmids of the U.S.A.)

Diatoms are single celled golden algae that are encased in glass-like shells (frustules) composed mostly of silica that are intricately marked and nearly indestructible. Although they vary greatly in size, the most commonly encountered diatoms are from 10 to 200 microns long. A micron is 1/1000 of a millimeter.

There are more than 200 genera of living diatoms and approximately 100,000 extant species (plus many more fossil forms). Diatoms occur in virtually every environment that contains water. This includes not only oceans, seas, lakes, ponds and streams, but also soil. This project will deal only with the freshwater varieties.

Live diatoms contain chloroplasts which allow them to photosynthesize. These structures are typically shades of brown and yellow but other hues can occur. Non-living specimens lose their internal structures quite rapidly, leaving only the colorless frustule. In this state the finely etched patterns of the frustules can be plainly seen and are extremely useful in the identification process.

Posted on April 22, 2013 11:33 PM by william_dembowski