Stylaria is a genus of globally distributed clitellates consisting of two recognized species with a difficult taxonomic history: Stylaria lacustris and Stylaria fossularis. The current species-level taxonomy of this genus is unclear due to variation in several morphological characters. To assess the amount of species-level diversity in Stylaria, an integrative approach using morphological investigations and genetic information was employed. I investigated the phylogenetics of this genus using three loci, two mitochondrial (cox1, and rrnL), and one nuclear (ITS) gene regions. Using several species delimitation tools, I was able to estimate the number of species in this group. Automatic barcode gap discovery, assemble species by automatic partitioning (ASAP), and the Geneious Prime Species delimitation package all delimited at least five species within Stylaria, Bayesian Poisson Tree Processes(bPTP) recovered at least six, and DELINEATE proposed only three species, all within S. fossularis. Morphologically, there seems to be no clear, consistent distinction between members of S. lacustris from Europe and S. lacustris from North America. Based on my morphological investigations and disagreement among species delimitation methods, I conservatively propose that the subclades discovered via phylogenetic analysis of mitochondrial and nuclear sequence data within S. lacustris represent population-level rather than species-level variation. However, there appear to be at least two previously unknown species in need of proper descriptions within the S. fossularis species complex. Within Stylaria, morphological criteria might be useless at the species level as there is a high level of intraspecific morphological variation. Analyses of sexual characteristics of this group could help further document any differences between populations of S. lacustris.