This spectacular darkfield photomicrograph of the diatom Arachnoidiscus ehrenbergi was captured on an Olympus microscope by Mortimer Abramowitz. The specimen was illuminated with a high numerical aperture darkfield condenser with immersion oil placed between the microscope slide and the objective and condenser front lenses.
Most diatoms are planktonic, but some are bottom dwellers or grow on other algae or plants.
They are single-celled organisms, but some live in colonies. Diatoms are important components of phytoplankton, serving as primary sources of food for zooplankton in both marine and freshwater habitats. Diatomaceous earth, a substance composed of fossil diatoms, is used in filters, insulation, abrasives, paints, and varnishes. These organisms usually reproduce asexually by cell division, the overlapping shell halves separate, and each secretes a smaller bottom half, decreasing in size with each division. Periodic spore formation serves to restore the diatom line to its original size.