Abstract The naviculopsid morphology, which consists of an arch across the minor axis of a basal ring with two corners and sides, is the simplest of the Cenozoic silicoflagellate skeletal designs that include an apical structure. This skeletal design is most often associated with the genus Naviculopsis (geologic range: middle Paleocene to early Miocene), but also occurs among other silicoflagellate genera. This paper interprets the evolutionary history for silicoflagellates of naviculopsid morphology, beginning with a group of large two-sided silicoflagellates from the late early Paleocene, recently placed in genus Pseudonaviculopsis, and ending with a late Miocene group of naviculopsid morphologies associated with Bachmnnocena diodon subsp. nodosa. Between these is Naviculopsis, which has more than twenty species recognized in deep sea sediments. A significant portion of the Naviculopsis taxa discussed in this paper are associated with plexus episodes of abundant and unusual variability from the late Paleocene, late Eocene and early Miocene. A possible explanation of the development of this skeletal morphology, as well as silicoflagellates with more complicated apical structures, is a need to decrease the size of portals, which may better support the cell boundary during mitosis.

中文翻译：

---

新生代硅鞭毛虫舟形动物骨骼形态的演变

摘要 舟形动物的形态由横跨基环短轴的拱形组成，具有两个角和边，是新生代硅鞭毛虫骨骼设计中最简单的，包括顶端结构。这种骨骼设计最常与 Naviculopsis 属（地质范围：中古新世到早中新世）有关，但也发生在其他硅鞭毛虫属中。本文解释了舟形动物形态的硅鞭毛虫的进化历史，从一组来自晚古新世晚期的大型双面硅鞭毛虫开始，最近被归入 Pseudonaviculopsis 属，并以与 Bachmnnocena diodon subsp. 相关的中新世晚期舟形藻类形态结束。结节 介于两者之间的是 Naviculopsis，它在深海沉积物中有 20 多种被认可的物种。本文中讨论的 Naviculopsis 分类群的很大一部分与来自晚古新世、晚始新世和早中新世的丰富和异常变异的丛集有关。这种骨骼形态以及具有更复杂顶端结构的硅鞭毛虫的发展的一个可能解释是需要减小门户的大小，这可能更好地支持有丝分裂期间的细胞边界。