Abstract Defining species boundaries or proposing synonymies remains a challenging task. In such cases, quantifying morphological or molecular variation provides critical support for developing robust taxonomic hypotheses. Within this framework, Geometric Morphometrics (GM) offers a quantitative and replicable approach for assessing shape variation. Here, we applied GM techniques to quantify variation in the apex and subapical tooth of the paramere (non-intromittent male genitalia) in selected species of Ranatra (Insecta: Hemiptera: Nepidae), aiming to clarify the taxonomic status of Ranatra bachmanni De Carlo, R. magna Kuitert, and R. macrophthalma Herrich-Schäffer, whose original descriptions were based solely on body size and coloration. A total of 100 male specimens were examined, including the holotypes of R. bachmanni and R. magna . Bidimensional shape data were obtained using four landmarks and 28 semi-landmarks plotted on the distal portion of the right paramere. The dataset was analyzed using exploratory approaches (boxplots, Principal Component Analysis PCA, ANOVA, and discriminant analysis CVA). While centroid size differed significantly among species, shape differences were not statistically significant. PCA revealed substantial morphospace overlap, and CVA correctly classified only 47.5% of the specimens. Additionally, shape exhibited residual allometric effects, with smaller parameres, more frequently observed in R. macrophthalma , tending to have shorter apices. However, considerable variation was still present, and no interspecific differences were detected in the subapical tooth. Our findings support the synonymy of R. bachmanni and R. magna with R. macrophthalma , highlighting the importance of GM in solving taxonomic uncertainties.
Barros et al. (Wed,) studied this question.