The diatom genera Licmophora and Fragilaria are frequent epiphytes on marine macroalgae and can be infected by intracellular parasitoids traditionally assigned to the oomycete genus Ectrogella. Much debate and uncertainty remains about the taxonomy of these oomycetes, not least due to their morphological and developmental plasticity. Here, we used single‐cell techniques to obtain partial sequences of the parasitoids 18S and cox2 genes. The former falls into two recently identified clades of Pseudo‐nitzschia parasites temporarily named OOM_1_2 and OOM_2, closely related to the genera of brown and red algal pathogens Anisolpidium and Olpidiopsis. A third group of sequences falls at the base of the red algal parasites assigned to Olpidiopsis. In one instance, two oomycete parasitoids seemed to co‐exist in a single diatom cell; this co‐occurrence of distinct parasitoid taxa not only within a population of diatom epiphytes, but also within the same host cell, possibly explains the ongoing confusion in the taxonomy of these parasitoids. We demonstrate the polyphyly of Licmophora parasitoids previously assigned to Ectrogella (sensu Sparrow, 1960) and show that parasites of red algae assigned to the genus Olpidiopsis are most likely not monophyletic. We conclude that combining single‐cell microscopy and molecular methods is necessary for their full characterisation.

中文翻译：

---

硅藻 Licmophora sp. 的“Ectrogella”寄生蜂。是多系的

硅藻属 Licmophora 和 Fragilaria 是海洋大型藻类上常见的附生植物，可以被传统上属于卵菌属 Ectrogella 的细胞内寄生物感染。关于这些卵菌的分类学仍然存在许多争论和不确定性，尤其是由于它们的形态和发育可塑性。在这里，我们使用单细胞技术获得了寄生蜂 18S 和 cox2 基因的部分序列。前者属于最近确定的两个 Pseudo-nitzschia 寄生虫进化枝，暂时命名为 OOM_1_2 和 OOM_2，与棕色和红色藻类病原体 Anisolpidium 和 Olpidiopsis 的属密切相关。第三组序列位于分配给 Olpidiopsis 的红藻寄生虫的基部。在一个例子中，两个卵菌寄生蜂似乎共存于一个硅藻细胞中；这种不同的寄生生物分类群不仅在硅藻附生植物种群中而且在同一宿主细胞内同时发生，这可能解释了这些寄生生物分类学的持续混乱。我们展示了先前分配给 Ectrogella (sensu Sparrow, 1960) 的 Licmophora parasitoids 的多系，并表明分配给 Olpidiopsis 属的红藻寄生虫很可能不是单系的。我们得出结论，结合单细胞显微镜和分子方法对于它们的完整表征是必要的。1960) 并表明分配给 Olpidiopsis 属的红藻寄生虫很可能不是单系的。我们得出结论，结合单细胞显微镜和分子方法对于它们的完整表征是必要的。1960) 并表明分配给 Olpidiopsis 属的红藻寄生虫很可能不是单系的。我们得出结论，结合单细胞显微镜和分子方法对于它们的完整表征是必要的。