Sexual reproductive cells and processes are highly conserved in a wide range of organisms. A specialized, expandable zygote called the auxospore is a cell known only in diatoms. Auxospores perform two critical functions in the life cycle of most diatoms: (1) as in other sexual organisms, they confer the benefits of genetic recombination to diatom progeny, and (2) restore larger cell size and allow a new cycle of vegetative cell size diminution to commence. Because of this dual importance in the diatom life cycle, the auxospore is strongly conserved, in contrast to the astounding diversity of forms among diatom vegetative cells. The auxospore is a complex cell which develops in a specific sequence of stages with a variety of characteristic structures recognizable across all diatoms. With only two major blueprints for auxospore growth and development (isodiametric and anisodiametric) and a number of highly conserved associated structures, studying this aspect of the diatom life cycle may reveal much about their deep evolutionary history. In the evolutionarily more recent arrivals (i.e., pennates), additional reproductive characters may be informative, e.g., mode of gamete motility, anisogamy vs. isogamy. We argue that combined with the widely varying but taxon-specific aspects of diatom gametogenetic processes, auxospores are excellent tools for cross group comparisons that provide insight into their evolutionary relationships. Expanding our dataset from 21 genera presented in 2004 to 65 polar centrics, nonpolar centrics, and araphid pennates, we repostulate that the evolutionarily informative capacity of auxospore development stands on its own.

性生殖细胞和过程在多种生物中高度保守。一种专门的，可扩展的合子称为毛孢子，是仅在硅藻中已知的细胞。辅助孢子在大多数硅藻的生命周期中执行两个关键功能：（1）与其他有性生物一样，它们将基因重组的好处赋予硅藻后代，（2）恢复较大的细胞大小并允许新的营养细胞大小循环缩小开始。由于在硅藻的生命周期中具有双重重要性，与硅藻营养细胞之间形式的惊人多样性相反，毛囊孢子被高度保守。毛孢子是一个复杂的细胞，它以特定的阶段顺序发育，具有可在所有硅藻上识别的多种特征结构。只有两个关于孢子生长和发育的主要蓝图（等径和非等径）以及许多高度保守的相关结构，研究硅藻生命周期的这一方面可能会揭示它们的深层进化历史。在进化上较新的到来者（即半月形）中，其他生殖特征可能是有益的，例如配子运动方式，同性与同性的对比。我们认为，结合硅藻配子发生过程的广泛变化但特定分类群方面，毛囊孢子是进行跨组比较的极佳工具，可提供对它们进化关系的洞察力。将我们的数据集从2004年提出的21个属扩展到65个极地中心，非极地中心和阿拉伯阿南半形体，