Benthic varieties can glide over the substrate on layer of mucus and planktonic varieties stay afloat using internal fat globules for buoyancy. Diatoms often appear to be brown. They produce oils and fatty acids as an end-product of the photosynthetic process. In areas where they are abundant this can create an oily slick on the surface of the water. They usually occur singly, but may also form chains held together by protoplasmic threads or strands of mucilage or spiny projections that lock together.
Some groups take stellate forms or make twisted spiral patterns.
Unlike radiolarians, they are easy to grow in the laboratory and more is understood about their reproductive biology and ontogeny. They usually reproduce by asexual division and when generations come rapidly, the average size of the population declines. The valves pull apart and each of the parent valves becomes the epivalve of the daughter cells. So half of the daughter population is constantly getting smaller. They multiply as often as once a day.