Large-scale phylogenomics of the genus Macrostomum (Platyhelminthes) reveals cryptic diversity and novel sexual traits

•94 of the 145 included species are new to science.•Across phylogenetic methods robust clades are recovered.•Exact branching pattern in the backbone of the phylogeny differs between inference methods.•Cryptic speciation occurs in one Macrostomum clade.•Sperm and male copulatory organ morphology is extremely diverse.