The diatoms may be derived from an ancestral cell in which siliceous scales on opposite sides of the cell enlarged as the valves, while other scales become the Girdle bands. Taxonomically, diatoms are divided into two groups based on the symmetry of the cells. The cell has vesicles that increase the deposition of silica creating a new valve girdle band. Vegetative cells are diploid, and gametes are the only haploid stages. Sexual reproduction differs in centric and pennates diatoms.
Centric diatoms undergo meiosis to form eggs and sperm.
Oogonial cells usually produces one egg, which may be released into the water or retained. Size decreases as mitosis proceeds. This provides a timing mechanism between sexual reproduction. Centric, antheridial cells meiosis produces 4 sperms or more per cell. Penate are cells not flagellate, gametangial cells pair in muscilage, and each cell undergoes meiosis.