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The protoplast of a diatom before formation of a siliceous cell wall occurs. Auxospores are usually formed following a sequence of vegetative cell divisions in which the daughter cells become progressively smaller. The decrease in size results from the nature of diatom cell division whereby the two halves of the cell separate, each half containing a daughter cell. A new half wall is then formed, the edges of which fit within those of the old half wall in a manner resembling a Petri dish. Thus the diatoms decrease in size until a certain limit is reached, at which point auxospores are released. The naked auxospores are free to expand before forming a cell wall. Auxospores may also form after sexual fusion or by apogamy or parthenogenesis.
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