Is ‘everything everywhere’? Unprecedented cryptic diversity in the cosmopolitan flatworm<i>Gyratrix hermaphroditus</i>

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