ABSTRACT Nearly two decades ago a scaly quadriflagellate culture was established from a sample collected in Golden Horn Bay, eastern Russia. Here we present a comparative analysis of pheno- and genotypic characters and show that the isolate did not match any existing species of Pyramimonas and is therefore described as P. tatianae sp. nov. The species was probably identified as P. aff. cordata in previous studies on material from the same area. Based on an ultrastructural account of the cell and its external body scales it was found to belong to the subgenus Vestigifera. This was supported by a phylogenetic analysis using the chloroplast-encoded rbcL gene. The cell dimensions of P. tatianae were 6–7 µm long and 5–6 µm wide and it thus represented one of the smaller species of the genus. The cup-shaped chloroplast was divided into four lobes reaching from the middle to the anterior part of the cell. A single posterior eyespot was observed adjacent to an excentric pyrenoid. The ultrastructure of the body and flagellar scales were illustrated from material prepared for whole mounts and thin sections. The new species was compared with P. cordata and P. mitra, two other vestigiferans with which it shares some morphological features. The sequence divergence between P. tatianae and the most closely related species, P. mitra, was 2.5%. The phylogeny of Vestigifera revealed two lineages, one comprising cold-water species and the cosmopolitan P. orientalis, and the other species from temperate-subtropical waters. The tree topology suggested a southbound dispersal route. This was further supported by all antarctic Pyramimonas species having encystment stages as part of their life cycle. It was therefore probable that their ancestors also were capable of producing cysts allowing transportation over great distances. A formal description of the class Pyramimonadophyceae comprising both extant and extinct species was also provided.

中文翻译：

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Pyramimonas tatianae sp. 的显微镜和系统发育。十一月 (Pyramimonadales, Chlorophyta)，一种来自金角湾（俄罗斯东部）的鳞状四鞭毛虫，对 Pyramimonadophyceae classis nova 的正式描述

摘要 近二十年前，从俄罗斯东部金角湾收集的样本中建立了鳞状四鞭毛虫培养物。在这里，我们对表型和基因型特征进行了比较分析，并表明该分离物与任何现有的 Pyramimonas 物种都不匹配，因此被描述为 P. tatianae sp。十一月 该物种可能被鉴定为 P. aff。cordata 在先前对同一地区材料的研究中。根据对细胞及其外部体鳞的超微结构描述，发现它属于 Vestigifera 亚属。这得到了使用叶绿体编码的 rbcL 基因的系统发育分析的支持。P. tatianae 的细胞尺寸为 6-7 µm 长和 5-6 µm 宽，因此它代表了该属中较小的物种之一。杯状叶绿体被分成四个叶，从细胞的中部到前部。在偏心核蛋白附近观察到单个后眼点。身体和鞭毛鳞片的超微结构是从为整个安装和薄片准备的材料中说明的。新物种与 P. cordata 和 P. mitra 进行了比较，这两种残留物与它共享一些形态特征。P. tatianae 与最密切相关的物种 P. mitra 之间的序列差异为 2.5%。Vestigifera 的系统发育揭示了两个谱系，一个包括冷水物种和世界性的 P.orientalis，另一个物种来自温带-亚热带水域。树形拓扑结构建议了一条南行的散布路线。这得到了所有具有包囊阶段作为其生命周期一部分的南极 Pyramimonas 物种的进一步支持。因此，他们的祖先很可能也能够产生允许远距离运输的包囊。还提供了包括现存和灭绝物种的 Pyramimonadophyceae 纲的正式描述。