Hyalosira gene sequences are divided into two clades within different families. We examined authentic material of Hyalosira (isotype material of H. obtusangula, synonymous with H. delicatula) and voucher specimens of published sequences, and pooled our observations of Hyalosira-like taxa from benthic and epizoic habitats in several parts of the globe. The two molecular clades corresponded to two morphological groups, with Hyalosira obtusangula associated with Grammatophoraceae. We emend the description and provide lectotypification for Hyalosira and propose Placosira to encompass the taxa in the other clade, associated with Rhabdonemataceae. We propose that Hyalosira has uniseriate to triseriate striae, sometimes different on valve face and mantle. Copulae in most species had shallow septa, though in one they were moderately deep. All species had girdle bands bearing two rows of areolae separated by a midrib. We name five new species of Hyalosira. Morphologies of taxa in the Placosira clade were superficially similar to Hyalosira but differed in having areolae with ricae, a single row of areolae on the girdle bands, and tubular rimoportulae on the valve-face-mantle junction. Hyalosira hustedtiana Patrick should revert to its original position in Striatella until the appropriate genus can be determined. We emend Rhabdonematales to encompass Rhabdonemataceae, Grammatophoraceae and Tabellariaceae.

Hyalosira基因序列在不同的家族中分为两个进化枝。我们检查了Hyalosira 的真实材料（H. obtusangula 的同种型材料，与H. delicatula同义）和已发表序列的凭证标本，并汇集了我们对来自全球多个地区的底栖和表生栖息地的类Hyalosira类群的观察结果。这两个分子进化枝对应于两个形态组，Hyalosira obtusangula与 Grammatophoraceae 相关。我们修改描述并为Hyalosira提供选型并提出Placosira包括与 Rhabdonemataceae 相关的另一个进化枝中的分类群。我们认为Hyalosira具有单列到三列的条纹，有时在瓣膜面和地幔上不同。大多数物种的 copulae 都有浅的隔膜，但在一个物种中它们是中等深的。所有物种的腰带都有两排被中脉隔开的乳晕。我们命名了Hyalosira 的五个新物种。Placosira进化枝中的分类群的形态在表面上与Hyalosira相似，但不同之处在于乳晕与 ricae、环带上的单排乳晕和瓣膜-面-地幔交界处的管状 rimoportulae。Hyalosira hustedtiana Patrick 应该恢复到其在条纹藻中的原始位置直到确定合适的属。我们将 Rhabdonematales 修正为包含 Rhabdonemataceae、Grammatophoraceae 和 Tabellariaceae。