Deep mitochondrial divergences were observed in Scandinavian populations of the terrestrial to semi-aquatic annelid Fridericia magna (Clitellata: Enchytraeidae). This raised the need for testing whether the taxon is a single species or a complex of cryptic species. A total of 62 specimens from 38 localities were included in the study, 44 of which were used for species delimitation. First, the 44 specimens were divided into clusters using ABGD (Automatic Barcode Gap Discovery) on two datasets, consisting of sequences of the mitochondrial markers COI and 16S. For each dataset, the worms were divided into six not completely congruent clusters. When they were combined, a maximum of seven clusters, or species hypotheses, were obtained, and the seven clusters were used as input in downstream analyses. We tested these hypotheses by constructing haplowebs for two nuclear markers, H3 and ITS, and in both haplowebs the specimens appeared as a single species. Multi-locus species delimitation analyses performed with the Bayesian BPP program also mainly supported a single species. Furthermore, no apparent morphological differences were found between the clusters. Two of the clusters were partially separated from each other and the other clusters, but not strongly enough to consider them as separate species. All 62 specimens were used to visualise the Scandinavian distribution, of the species, and to compare with published COI data from other Fridericia species. We show that the morphospecies Fridericia magna is a single species, harbouring several distinct mitochondrial clusters. There is partial genetic separation between some of them, which may be interpreted as incipient speciation. The study shows the importance of rigorous species delimitation using several independent markers when deep mitochondrial divergences might give the false impression of cryptic speciation.

中文翻译：

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测试物种假说：巨大的线虫蠕虫Fridericia magna（线虫）（Annelida：Clitellata），线粒体变异很大。

在陆生至半水类甲虫Fridericia magna（Clitellata：Enchytraeidae）的斯堪的纳维亚种群中观察到深线粒体差异。这就需要测试分类单元是单个物种还是复杂物种。该研究共包括38个地区的62个标本，其中44个用于物种划界。首先，使用ABGD（自动条形码间隙发现）在两个数据集上将44个样本分成簇，该数据集由线粒体标记COI和16S的序列组成。对于每个数据集，蠕虫被分为六个不完全一致的簇。当它们组合在一起时，最多获得七个聚类或物种假设，并将七个聚类用作下游分析的输入。我们通过构建两个核标记物H3和ITS的单倍网来检验这些假设，并且在两个单倍网中标本都表现为单个物种。用贝叶斯BPP程序进行的多位点物种划界分析也主要支持单个物种。此外，在簇之间没有发现明显的形态学差异。其中两个集群彼此之间部分隔离，而其他集群则不足以将其视为独立的物种。所有62个标本都用于可视化该物种的斯堪的纳维亚分布，并与其他Fridericia物种的已公布COI数据进行比较。我们表明，形态物种大凤蝶是一个单一的物种，拥有几个不同的线粒体簇。其中一些之间存在部分遗传分离，可以解释为初期物种。研究表明，当线粒体的深层差异可能给人以隐性物种的错误印象时，使用几个独立的标记对物种进行严格分隔的重要性。