Melosira varians is a centric diatom with typical oogamous reproduction. Vegetative cells (2n in the diatoms) become gradually smaller through repeated cell divisions and conservation of the cell walls to produce the epivalves of the two daughter cells. Certain of the very small cells in the population signal others to prepare for reduction division. Meiosis produces a single egg with a haploid nucleus after the degeneration of the other three nuclei. The four motile sperm arise from the antheridial cell following meiosis. Fusion forms a zygote, which enlarges as an auxospore. Germination of the auxospore yields the largest vegetative cell for the species (the initial cell).