In Opiliones, one of the largest orders within the class Arachnida, with more than 6000 described species, sexual dimorphism can be widespread and exaggerated. This great variety of forms of gender-based dimorphism suggests that sexual selection may play an important role in the diversification of some lineages. It also impacts species identification, assignment of females to described species and biodiversity assessments. Here we use DNA-sequence-based species discovery methods (the Poisson Tree Processes model with Bayesian support values, bPTP, and the Generalized Mixed Yule–Coalescent approach, GMYC, accounting for phylogenetic uncertainty) to shed light on the morphological disparity displayed in several species of neopilionid harvestmen from New Zealand. Both species delimitation analyses recovered many clades that coincide with our prior assignment of morphospecies, based solely on males, and allowed us to assign females and juveniles to these species as well as to identify putative new species and to assign some unidentified species to genera. Several genetic species, particularly Forsteropsalis inconstans and Pantopsalis cheliceroides-listeri, showed complex morphological disparity in the size and shape of the male chelicerae, but also in the general size and coloration patterns of the males. The systematic implications of our results and a possible ecological explanation for the exaggerated traits are discussed. Following our findings, the following taxonomic action is taken: Forsteropsalis nigra is considered a junior synonym of F. inconstans (new synonymy).