Bioacoustics of Dugesia repanda

Discussion. Dugesia repanda is readily distinguished from its congeners by its most striking characteristic, viz., the dorsally positioned opening of the ejaculatory duct on the penis papilla. This feature is highly distinctive and allows for immediate differentiation from other species within the genus. To date, such a trait has been documented only for D. umbonata Song & Wang, 2020 , D. majuscula Chen & Dong, 2021 , D. tumida Chen & Sluys, 2022 , and D. saccaria A.-T. Wang & Sluys, 2024 ( Song et al. 2020 ; Wang et al. 2021b ; Wang et al. 2022 ; Zeng et al. 2024 ). In D. umbonata , D. majuscula , and D. saccaria , the oviducts open asymmetrically into the copulatory apparatus, whereas D. tumida and D. repanda exhibit symmetrical oviducal openings. However, D. tumida possesses a penis papilla equipped with a large, symmetrical penial valve from which a narrow, distal portion of the papilla emerges—an arrangement that is entirely absent in D. repanda . Additionally, D. umbonata and D. saccaria feature a prominent, muscular swelling on the bursal canal, a structure not present in D. repanda . Finally, D. repanda is further distinguished by the presence of a dorsal penial fold that projects into the male atrium, a feature absent in the aforementioned congeners. Furthermore, the molecular analysis revealed that phylogenetically D. repanda is far removed from D. majuscula , D. tumida , D. saccaria , and D. umbonata ( Fig. 2 ). The dorsal penial fold observed in D. repanda is similar to those found in several congeners (cf. Stocchino et al. 2017 , table 4), but all of these species are structurally different from D. repanda . A noteworthy feature of D. repanda concerns its exceptionally elongated seminal vesicle that is enclosed by a strong coat of muscles and with its major portion being located considerably anterior to the root of the penis papilla. This is a rather rare characteristic that has been documented also for D. didiaphragma De Vries, 1988 , D. pustulata Harrath & Sluys, 2019 , and D. ectophysa Marcus, 1953 ( Marcus 1953 ; De Vries 1988 ; Harrath et al. 2019 ). Nevertheless, D. repanda remains unequivocally distinguishable from these congeners by its completely different penis papilla.