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Why do diatoms become smaller during repeated cell divisions?

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“mermaid's wine glass” algae — Algae The macroscopic genus of algae known as *Acetabularia* is commonly called “mermaid's wine glass” because of the distinctive umbrella-like shape of the tips of its stalks.

Diatoms possess a rigid, pillbox-like cell wall known as a frustule, which consists of two overlapping halves called the epitheca and the hypotheca.1

During cell division, these two overlapping halves separate, and each half serves as a template for the formation of a new, smaller bottom valve. Because the new valves are formed within the existing shell, they are generally smaller than the original parent valves. Consequently, with each successive generation, the average size of the diatom population progressively decreases.12

To restore the diatom line to its original size, the organisms undergo a process involving spore formation. When diatoms reach a critically small size, sexual reproduction is often stimulated, leading to the formation of an auxospore. This specialized cell grows significantly in size before dividing to produce new, larger vegetative cells, effectively resetting the size of the organism.12