Cryptic diversity in supposedly species-poor genera of Enchytraeidae (Annelida: Clitellata)

Using a two-step workflow, we test the species boundaries in three genera of enchytraeid worms, Globulidrilus, Hemifridericia and Stercutus (Clitellata: Enchytraeidae), which contains one to three nominal species each. For the species discovery phase, DNA barcode-based clustering analyses in ABGD (Automatic Barcode Gap Discovery) are performed, using mitochondrial cytochrome c oxidase subunit I (COI) data. The clusters from these analyses are then used as input in the species validation phase, where multispecies coalescent-based multilocus species delimitation analyses are performed in BPP (Bayesian Phylogenetics and Phylogeography) using nuclear Histone 3 (H3) and Internal Transcribed Spacer (ITS) data. For all BPP analyses, several species delimitation arrangements are included in the 95% credibility interval, and no complete sets of species are well supported. However, we conclude that our data set comprises at least seven species of Globulidrilus, all attributed to the nominal morpho-species G. riparius, three species of Hemifridericia, whereof two are cryptic lineages within H. parva and one is H. bivesiculata, and at least six species of the previously monotypic Stercutus. The species are not formally described here due to a lack of mature specimens of many of them in combination with low support for some of them in the genetic analyses. However, this is the first step towards a better understanding of the diversity within these groups.