Radial and pennate diatoms as seen under a microscope with darkfield illumination. Diatoms are protists which have shells sculpted out of silicon oxide. After the living protist has perished the shells remain. These clear shells are comprised of two halves called valves. Diatom shells and their corresponding patterns respond to beautifully and artfully to a variety of colorful microscopic illumination techniques. Many are so intricately detailed that they have long been used as test objects for microscope objectives.
There are two major classes of diatoms: centric and pennate. Centric diatoms have patterns arranged radially, around a central point, known as radial symmetry. Pennate diatoms have bilateral symmetry, left and right matching halves, and are generally needle or boat shaped.
When alive, diatoms are brownish green in color a live almost everywhere, from open waters to quiet shallows. They may live alone or in colonies.
In the mid to late 19th century Victorian era mounters created patterns of them on microscope slides using micro manipulators. Diatoms are a favorite of microscopists for their beauty. Originally they were used for testing the resolving power of objectives. These are highly sought after.
Kingdom: Protists, Phylum: Bacillariophyta
Photomicroscope I on Ektachrome Tungsten 35mm color film, with various illuminations and colors at 80X, 160x on a 4x6 inch print.