Hemiodus is the largest genus of the South American freshwater fish family Hemiodontidae, with 23 valid species. However, the species‐level diversity of Hemiodus remains uncertain since morphological studies have indicated additional species. Also, the phylogenetic relationships among species and species boundaries within this genus are still unresolved. Herein, we sequenced the barcode (COI) gene of 19 species of Hemiodus on which undertook molecular species delimitation methods (automatic barcode gap discovery [ABGD], generalized mixed Yule coalescent [GMYC] and Poisson tree process [PTP]) and the standard DNA barcoding procedure to establish species boundaries and cast light on putative new species in the genus. We also provide a COI‐based phylogenetic hypothesis for Hemiodus by maximum‐likelihood (ML) analysis, the first at species level. The results of ABGD, GMYC and PTP indicate that around 30 MOTUs (range: 28–32) exist for Hemiodus within our data set of 19 valid species with concordance among strategies (i.e. equal results) in delimiting 24 MOTUs. Using classical DNA barcoding procedures, we settled on 28 MOTUs for Hemiodus. Undescribed morphospecies (i.e. feasible for description or taxonomic validation), as well as cryptic species (i.e. lineages with high genetic distance but indistinguishable in external morphology), are proposed. Even with the limitations of a single‐locus phylogeny, the ML tree recovered many species and species groups as clades, corroborating, thus, their taxonomic separation. Overall, our results highlight the existence of an overlooked diversity of mitochondrial lineages in Hemiodus that can represent cryptic or poorly scrutinized species. Moreover, this study provides a molecular backbone for future studies on the systematics and evolution of Hemiodontidae taxa.

中文翻译：

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被忽视的线虫谱系中的线粒体谱系的生物多样性（Ostariophysi，Characiformes）

Hemiodus是南美淡水鱼类科Hemiodontidae的最大属，有23种有效物种。但是，由于形态学研究表明还有其他种类，所以Hemiodus的物种水平多样性仍然不确定。同样，该属内的物种和物种边界之间的系统发育关系仍未解决。在本文中，我们对19种Hemiodus的条形码（COI）基因进行了测序，在该基因上进行了分子物种定界方法（自动条形码间隙发现[ABGD]，广义混合Yule聚结[GMYC]和泊松树过程[PTP]）和标准DNA条形码程序以建立物种边界，并为该属中假定的新物种提供照明。我们还提供了基于COI的系统发生假说Hemiodus通过最大似然（ML）的分析中，第一在物种水平。ABGD，GMYC和PTP的结果表明，在我们的19个有效物种的数据集中，大约有30个MOTU（28-32个范围）存在于Hemiodus中，在界定24个MOTU的策略（即相等结果）之间保持一致。使用经典的DNA条形码程序，我们为Hemiodus确定了28个MOTU。提出了未描述的形态学物种（即，可用于描述或分类学验证）以及隐秘物种（即，具有高遗传距离但在外部形态学上无法区分的谱系）。即使受到单一基因座系统发育的限制，ML树也可以将许多物种和物种组作为进化枝恢复，从而确证了它们的分类学分离。总体而言，我们的研究结果突显了Hemiodus中存在着线粒体谱系的一种被忽视的多样性，它可以代表隐秘或审查不力的物种。此外，这项研究为今后对拟齿科分类系统的研究和发展提供了分子基础。