The valves often bear radially symmetrical ornamental patterns that can appear as dots when viewed with an optical microscope. Some also bear spines on their valves, which may either increase cell surface area and reduce sinking, or act as a deterrent to zooplankton grazers. Unlike pennate diatoms, centric diatoms never have a raphe.
On the valves of these organisms, radially symmetrical patterns are common, appearing as dots when viewed with an optical microscope. Some valves might have spines that could increase cell surface area and reduce sinking, or serve as a defense against zooplankton predators. Unlike pennate diatoms, centric diatoms never possess a raphe.