Abstract: In this study, geometric morphometrics was applied to quantify the morphology of central hamuli in sevenPolystomaspecies parasitizing hosts exhibiting terrestrial or arboreal adult habits. Results showed that central hamulus morphology provided a reliable character for species discrimination. More importantly, the analysis revealed that host habitat—an ecological factor acting directly on the parasite—exerted a significant shaping effect on hamulus morphology, thereby offering indirect evidence for the adaptive processes of the parasite to its host. This work not only addressed the gap in morphological adaptation studies of anuran-parasitizing monogeneans from arboreal and terrestrial hosts, but also contributed to a deeper understanding of host-parasite interaction mechanisms.

Key words: geometric morphometrics;Polystoma, central hamuli, morphological variation, habitat, ecological driver