Opalinids are a large group of anaerobic protists, mainly inhabiting the cloacae of amphibians (frogs and toads). The classification of this group has not been fully resolved, because of a lack of molecular information. Here, we give a redescription of Opalina triangulata Metcalf, 1923, collected from the rectum of the frog Fejervarya limnocharis, based on detailed morphological and molecular data. Our phylogenetic analyses confirmed the monophyly of Opalinata. Within it, Opalinea were monophyletic with O. triangulata and O. undulata as well as two Protoopalina species grouping together. Karotomorpha and Proteromonas did not group together confirming the paraphyly of Proteromonadea. Meanwhile, the ITS2 secondary structural similarities as well as G-C content revealed greater similitudes between Opalina species and P. lacertae than with Blastocystis hominis, which is in accordance with their position as sister clades in the SSU rDNA-based phylogenies.

蛋白石是一大批厌氧生物，主要栖息于两栖动物的泄殖腔（青蛙和蟾蜍）。由于缺乏分子信息，该组的分类尚未完全解决。在这里，我们根据详细的形态学和分子数据，对从青蛙Fejervarya limnocharis的直肠收集的1923年的Opalina triangulata Metcalf进行了重新描述。我们的系统发育分析证实了Opalinata的单性。在其中，Opalinea与O. triangulata和O. undulata以及两个Protoopalina物种一起分组。核形态和原核并没有一起确认Proteromonadea的附生生物。同时，ITS2的二级结构相似性以及GC含量显示，Opalina物种和P. lacertae之间的相似性比人乳杆菌（Blastocystis hominis）更好，这与其在基于SSU rDNA的系统进化中作为姐妹进化枝的位置相符。