Ventrifissura is a group of poorly studied heterotrophic biflagellates in the phylum Cercozoa. Despite a phylogenetic placement with only weak support and a lack of ultrastructural data, Ventrifissura was assigned to Thecofilosea. In the presented study, we established cultures of two novel species of Ventrifissura (V. oblonga n. sp. and V. velata n. sp.) isolated from coastal marine environments in Japan, and performed light and electron microscopy observations and molecular phylogenetic analysis. Transmission electron microscopy revealed that V. oblonga shares several ultrastructural characteristics with thecofilosean flagellates, including permanently condensed chromosomes, a extracellular theca, and slender extrusomes. Molecular phylogenetic analysis could not resolve the phylogenetic position, but the possibility that Ventrifissura clusters into Ventrifilosa was supported by approximately unbiased tests. Based on both morphological and phylogenetic findings, we concluded that Ventrifissura is a basal lineage of Thecofilosea.

Ventrifissura是一组在Cercozoa门中研究不多的异养双鞭毛虫。尽管在系统发育上只有很少的支持和缺乏超微结构数据，但文特里弗拉被指定为Thecofilosea。在所提出的研究中，我们建立了两个新种培养物Ventrifissura（V。桲ñ。属和V。velata ñ。物种）在日本沿海环境隔离，并且进行光学和电子显微镜的观察和分子进化分析。透射电子显微镜显示，V。长方形具有与cofilosean鞭毛虫相同的几个超微结构特征，包括永久浓缩的染色体，细胞外卵泡膜和纤细的挤出物。分子系统发育分析不能解析系统发育的位置，但是几乎无偏的试验支持了文氏菌群聚入Ventrifilosa的可能性。基于形态学和系统发育学发现，我们得出结论，文氏酵母是Thecofilosea的基础谱系。