The diatom cell wall is made up by two half shells like a petri dish, named epitheca and hypotheca, that together tightly enclose the protoplast.

After cleavage of the protoplast, the resulting daughter protoplasts are trapped within the mother cell wall -  (1). A small intracellular vesicle, named silica deposition vesicle (SDV), is formed in both the daughter protoplasts. The SDV can be regarded as a cellular ”reaction vessel” that is responsible for controlling silica precipitation and for moulding the precipitating silica to yield the ornate patterns characteristic for the respective diatom species.

The SDV enlarges as more and more silica is deposited - (2).

After completion of the silica forming/patterning process, the new valves are transferred to the extracellular space in a remarkable exocytotic process - (3).

Thus, the characteristic cell wall patterns of a diatom species are likely to depend on species specific supramolecular assemblies inside the  SDV.