The bacillariophyceae, popularly called diatoms, form a very important group of both fresh water and marine unicellular algae. There are about 16000 species of algae present in this group.The shape and size of these algae vary greatly. This may be in the form of boots, circles, triangles, squares etc. Sometimes the unicellular forms unite by a gelatinous material to form small colonies.
Example of Bacillariophyceae
Example: Cyclotella, Isthmia, Rutilaria, Corethron
Example: Fragilaria, Navicula, Eunotia, Epithemia, Pinnularia