Eupelagonemids, formerly known as Deep Sea Pelagic Diplonemids I (DSPD I), are among the most abundant and diverse heterotrophic protists in the deep ocean, but little else is known about their ecology, evolution, or biology in general. Originally recognized solely as a large clade of environmental ribosomal subunit RNA gene sequences (SSU rRNA), branching with a smaller sister group DSPD II, they were postulated to be diplonemids, a poorly-studied branch of Euglenozoa. Although new diplonemids have been cultivated and studied in depth in recent years, the lack of cultured eupelagonemids has limited data to a handful of light micrographs, partial SSU rRNA gene sequences, a small number of genes from single amplified genomes (SAGs), and only a single formal described species, Eupelagonema oceanica. To determine exactly where this clade goes in the tree of eukaryotes and begin to address the overall absence of biological information about this apparently ecologically important group, we conducted single-cell transcriptomics from two eupelagonemid cells. A SSU rRNA gene phylogeny shows these two cells represent distinct subclades within eupelagonemids, each different from E. oceanica. Phylogenomic analysis based on a 125-gene matrix contrasts with the findings based on ecological survey data, and shows eupelagonemids branch sister to the diplonemid subgroup Hemistasiidae.

中文翻译：

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eupelagonemids、丰富多样的深海异养生物的系统发育位置

Eupelagonemids，以前称为深海中上层双龙鱼 I (DSPD I)，是深海中数量最多、种类最多的异养原生生物之一，但人们对它们的生态、进化或生物学知之甚少。最初仅被认为是环境核糖体亚基 RNA 基因序列 (SSU rRNA) 的一个大进化枝，与一个较小的姐妹群 DSPD II 分支，它们被认为是双克隆动物，这是眼虫动物门的一个研究很少的分支。尽管近年来新的双倍酮类动物已被培养和深入研究，但由于缺乏培养的真双倍酮类动物，数据仅限于少数光学显微照片、部分 SSU rRNA 基因序列、来自单一扩增基因组 (SAG) 的少量基因，并且仅单一正式描述的物种，Eupelagonema oceanica。为了准确确定这个进化枝在真核生物树中的位置，并开始解决这个显然具有重要生态意义的群体的生物信息的整体缺失问题，我们对两个真核素细胞进行了单细胞转录组学。SSU rRNA 基因系统发育表明，这两种细胞代表了 eupelagonemids 中不同的亚支，每个亚支均不同于 E. oceanica。基于 125 个基因矩阵的系统发育基因组分析与基于生态调查数据的结果进行对比，并显示真虫科是双克隆亚群 Hemistasiidae 的姐妹。