Diatoms are classified in different forms which depend from class to division. Sometimes it's called Bacillariophyceae and even Diatomophyceae as well. But apart from these traditionally diatoms are divided into two classes which are centric diatoms and pennate diatoms. In this centric diatoms are said to be radially symmetric and pennate diatoms are bilaterally symmetric. Recent revisions divide diatoms into three classes: centric diatoms (Coscinodiscophyceae), pennate diatoms without a raphe (Fragilariophyceae), and pennate diatoms with a raphe (Bacillariophyceae).