sentences:  The order is named for the shape of the cell walls (or valves or frustules) of centric diatoms, which are circular or ellipsoid in valve view.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.