Euglenophyceae are unicellular algae with the majority of their diversity known from small freshwater reservoirs. Only two dozen species have been described to occur in marine habitats, but their abundance and diversity remain unexplored. Phylogenetic studies revealed marine prasinophyte green alga, Pyramimonas parkeae, as the closest extant relative of the euglenophytes' plastid, but similarly to euglenophytes, our knowledge about the diversity of Pyramimonadales is limited. Here we explored Euglenophyceae and Pyramimonadales phylogenetic diversity in marine environmental samples. We yielded 18S rDNA and plastid 16S rDNA sequences deposited in public repositories and reconstructed Euglenophyceae reference trees. We searched high‐throughput environmental sequences from the TARA Oceans expedition and Ocean Sampling Day initiative for 18S rDNA and 16S rDNA, placed them in the phylogenetic context and estimated their relative abundances. To avoid polymerase chain reaction (PCR) bias, we also exploited metagenomic data from the TARA Oceans expedition for the presence of rRNA sequences from these groups. Finally, we targeted these protists in coastal samples by specific PCR amplification of two parts of the plastid genome uniquely shared between euglenids and Pyramimonadales. All approaches revealed previously undetected, but relatively low‐abundant lineages of marine Euglenophyceae. Surprisingly, some of those lineages are branching within the freshwater or brackish genera.

中文翻译：

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对环境序列和叶绿体基因组的两个区域的分析表明，在海洋环境中存在新的光合桉树进化枝。

裸藻科是单细胞藻类，其大部分多样性都来自小型淡水水库。据描述，只有二十多种物种存在于海洋生境中，但其丰富性和多样性尚未得到开发。系统发育研究表明，海洋藻类绿藻，Pyramimonas parkeae，作为裸藻类植物质体最接近的现存亲戚，但与裸藻类植物相似，我们对金字塔形藻多样性的了解是有限的。在这里，我们探索了海洋环境样品中的裸藻目科和吡虫科的系统发育多样性。我们产生了18S rDNA和质体16S rDNA序列，这些序列存放在公共存储库中，并重建了裸藻科参考树。我们从TARA海洋考察和海洋采样日计划中搜索了18S rDNA和16S rDNA的高通量环境序列，并将它们置于系统发育背景中，并估计了它们的相对丰度。为了避免聚合酶链反应（PCR）的偏倚，我们还利用了来自TARA Oceans探险队的宏基因组学数据来确定这些组中存在rRNA序列。最后，我们通过特异性PCR扩增了桉树类和吡虫类之间唯一共享的质体基因组的两个部分，将沿海地区的这些原生生物定为目标。所有方法都揭示了以前未发现过但相对较少的海洋裸藻科谱系。出乎意料的是，其中一些谱系在淡水或微咸属中分支。