Many nominal species of microscopic animals traditionally fitting the ‘everything is everywhere’ paradigm have been revealed to be complexes of cryptic species. Here, we explore species diversity within the micrometazoan flatworm Gyratrix hermaphroditus—unique among meiofauna because of its global occurrence in a wide variety of brackish, freshwater and marine environments. With maximum likelihood and Bayesian approaches, we analysed 18S, 28S, 5.8S and ITS2 rDNA sequences from 401 specimens across the global distribution of G. hermaphroditus. Generalized Mixed Yule Coalescent (GMYC) and Automatic Barcode Gap Discovery (ABGD) methods delineated 78 and 62 putative species, respectively. This renders G. hermaphroditus one of the most species-rich complexes known to date. Based on shape variations of the male copulatory organ, 14 morphotypes corresponding with molecular clades were identified within the species complex. Within morphotypes, morphometric measurements were able to further discriminate between GMYC species using discriminant analyses. While most putative species occur on local or regional scales, over 10% are distributed over vast distances (>500 km apart) and two GMYC and six ABGD species have colonised multiple continents. This suggests that the cosmopolitanism of the G. hermaphroditus species complex is not just caused by mixing cryptic species with a more limited geographic distribution, but is due to the presence of previously unrecognised cosmopolitan taxa. The wide variation in distribution patterns between putative species indicates that meiofaunal biogeography should not be simplified into ‘everything is everywhere’, but rather entails every ecological state, extending from local endemism to true cosmopolitanism.

中文翻译：

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是“无处不在”吗？世界性扁虫 Gyratrix hermaphroditus 中前所未有的神秘多样性

许多传统上符合“无处不在”范式的微观动物的名义物种已被揭示为神秘物种的复合体。在这里，我们探索了微后生动物扁虫Gyratrix hermaphroditus 的物种多样性——它在小型动物群中是独一无二的，因为它在各种咸水、淡水和海洋环境中全球发生。使用最大似然和贝叶斯方法，我们分析了来自G. hermaphroditus全球分布的 401 个标本的 18S、28S、5.8S 和 ITS2 rDNA 序列。广义混合圣诞聚结 (GMYC) 和自动条码间隙发现 (ABGD) 方法分别描绘了 78 和 62 种推定物种。这使得G. hermaphroditus迄今为止已知的物种最丰富的复合体之一。根据雄性交配器官的形状变化，在物种复合体中确定了与分子进化枝相对应的 14 种形态类型。在形态类型中，形态测量能够使用判别分析进一步区分 GMYC 物种。虽然大多数假定的物种发生在局部或区域范围内，但超过 10% 的物种分布在很远的距离（相距 > 500 公里），并且两个 GMYC 和六个 ABGD 物种已经在多个大陆上定居。这表明G. hermaphroditus的世界主义物种复杂不仅是由地理分布更有限的隐秘物种混合引起的，而且是由于以前未被认识的世界性分类群的存在。假定物种之间分布模式的广泛差异表明小型动物生物地理学不应该被简化为“无处不在”，而是需要每个生态状态，从地方特有性延伸到真正的世界主义。