Coscinodiscophyceae is similar to Centrales. Order Centrales is a traditional, paraphyletic subdivision of the heterokontalgae known as diatoms. 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. Unlike pennate diatoms, centric diatoms never have a raphe.
In some taxonomy schemes, the centric diatoms are known instead as Order Coscinodiscophyceae. And in some schemes as order Biddulphiales. However, diatom taxonomy is changing due to the development of new molecular and genetical analysis tools.