Pleurostomatid ciliates, as a highly diverse and widely distributed unicellular eukaryote group, play a crucial role in the cycling of nutrients and energy in microbial food webs. However, research on pleurostomatids remains insufficient, resulting in a paucity of molecular information and substantial gaps in knowledge of their phylogenetic relationships. In recent years, we investigated pleurostomatid diversity in various Chinese habitats, including their systematic relationships and taxonomic circumscriptions, which were comprehensively analyzed using an integrative morphomolecular approach. Results revealed that: (1) pleurostomatids can be categorized into two suborders, Protolitonotina subord. nov. and Amphileptina Jankowski, 1967; (2) Protolitonotina subord. nov. represents the ancestral pleurostomatid group and includes two genera, Protolitonotus and Heterolitonotus gen. nov., characterized by right kineties progressively shortened along rightmost full kineties and absence of a left dorsolateral kinety; (3) Heterolitonotus gen. nov. represents an orphan lineage and is defined by an oral slit extending to its dorsal margin; (4) " Protolitonotus clampi" does not group with congeners but instead represents an orphan lineage, thus Novilitonotus gen. nov. is established to which P. clampi is transferred as Novilitonotus clampi comb. nov.; (5) three new species, Apoamphileptus paraclaparedii sp. nov., Heterolitonotus rex gen. nov., sp. nov., and Loxophyllum apohelus sp. nov., are described; and (6) helices 21es6a to 21es6d within the V4 region of small subunit ribosomal RNA (SSU rRNA) may serve as a useful tool for discriminating pleurostomatids. The evolutionary relationships among all main lineages of pleurostomatids are discussed and a key to the identification of pleurostomatid genera is provided.
侧口目纤毛虫是一类高度多样、分布广泛的单细胞真核生物，在水体微食物网的能量流动、物质循环等方面发挥着枢纽作用。囿于多种原因，当前该类群（特别是淡水湿地中）的研究严重不足，分子信息大量缺失，系统发育关系尚存诸多不明和混乱。为此，在过去的数年间，作者团队围绕该类群对多种生境开展了物种多样性研究，并借助整合分类学手段对其系统发育关系和分类阶元的刻画进行了深入分析。结果表明：（1）侧口目应分为两个亚目，分别为该文新建立原漫游亚目（Protolitonotina subord. nov.）和囊括核心类群的裂口亚目（Amphilpetina Jankowski, 1967）；（2）原漫游新亚目代表着低级分化、最原始的类群，其最突出的特征为：右侧动基列沿最右侧的完整体动基列依次逐渐缩短，同时缺失左侧背缘最外侧的动基列；（3）文内建立的异漫游虫新属（ Heterolitonotus gen. nov.）为侧口目中一个独立的支系，其口区极为特别：由整个腹缘延伸至背缘；（4）系统树显示“克兰姆原漫游虫”代表了一个单独的支系，其纤毛图式亦显示与目前的已知属种均构成了明确的差异，故以此为模式，建议建立一新属，新漫游虫属 Novilitonotus gen. nov., 由此将克兰姆原漫游虫新组合为克兰姆新漫游虫 Novilitonotus clampi comb. nov.；（5）本文同时描述了三个新种，拟克氏后裂口虫，霸王异漫游虫和偏绿斜叶虫；（6）基于SSU rRNA基因构建的二级结构显示，V4区域中的螺旋结构21es6a至21es6d可用于区分侧口目内的不同科属级类群。此外，该研究在综合信息基础上，对侧口目内部阶元进行了探讨和演化关系的新推测，并给出了一份到属级阶元的检索表。.
Keywords: Ciliates; Integrative approaches; New suborder; Phylogeny; Pleurostomatids.