Dugesia repanda Chen & Dong 2026, sp. nov.
Year: 2026
Type: article
Abstract: Dugesia repanda Chen & Dong, sp. nov. urn:lsid:zoobank.org:act: EA4BE002-5233-4D53-B130-22603DEE070C Habitat and Reproduction. Specimens were collected from a mountain stream adjacent to a roadside near the Sino-Vietnamese border, at an elevation of 860 m above sea level. The collection site is characterized by steep mountain slopes on one side of the road. The stream originates from mountain runoff, with recorded environmental conditions of 23.6°C air temperature and 19.4°C water temperature. The habitat featured dense riparian vegetation, abundant aquatic mosses, and a substrate primarily composed of stones in areas with slow currents (Fig. 3A, B). In situ observations revealed a high population density of planarians on the undersides of submerged stones, including numerous sexually mature individuals. Approximately half of the planarians collected from the wild were sexually mature. During laboratory culture, asexual individuals did not reproduce by fission, but, instead, gradually developed reproductive organs, reaching full maturity within two months. Notably, no cocoons were observed in field-collected specimens collected in October, and no cocoon deposition was observed during laboratory culture. Material examined. Holotype: ZMHNU-GTZ3, Pingbian Miao Autonomous County, Honghe Hani and Yi Autonomous Prefecture, Yunnan Province, China, 22°58'44"N, 103°51'48"E, 21 October 2024, coll. G-W. Chen, Z-M. Dong, F. Wu and coworkers, sagittal sections on 15 slides. Paratypes: ZMHNU-GTZ1, 2, 4, 5, 9, 12, ibid., sagittal sections on 23, 20, 15, 16, 10, and 10 slides, respectively; ZMHNU-GTZ7 and 11, ibid., transverse sections on 16 and 13 slides; ZMHNU-GTZ6, ibid., horizontal sections on 5 slides; RMNH.VER.22786.1, ibid., sagittal sections on 18 slides; RMNH.VER.22786.2, ibid., sagittal sections on 14 slides. Etymology. The specific epithet is derived from the Latin adjective repandus, bent backwards, turned up, alluding to the upward curved tip of the penis papilla. Diagnosis. Dugesia repanda is characterized by the following features: symmetrical openings of the oviducts into the bursal canal; an upward curving, highly asymmetrical penis papilla; highly elongated and muscularised seminal vesicle of which the major portion is located considerably anterior to the root of the penis papilla; a long connecting duct between the seminal vesicle and diaphragm; a dorsally located penial fold; ejaculatory duct opening subterminally through the dorsal wall of the penis papilla, the latter facing the dorsal body surface. Description. Live sexual specimens 13.89–17.74 mm long, 1.43–1.84 mm wide; asexual specimens 11.17– 14. 13 mm long, 1.32–1.56 mm wide. Head acutely triangular, with obtusely pointed auricles, eyes two, situated in pigment-free patches. Dorsal surface light yellowish (Fig. 3C); ventral surface pale yellow. Pharynx situated centrally, measuring about one-quarter of body length; outer pharyngeal musculature comprising subepithelial longitudinal layer and thin circular layer; additional inner longitudinal layer absent. Inner pharyngeal musculature consisting of thick subepithelial circular layer and thin longitudinal layer. Ovaries oval-shaped, occupying about one-third of the dorso-ventral space, situated immediately behind brain, at about one-sixth of distance between brain and pharynx root. Oviducts arising dorsally from ovaries, running ventro-posteriorly to level of the gonopore, then turning dorso-medially and opening symmetrically through lateral walls of bursal canal at its communication with common atrium. Shell glands erythrophilic, opening into vaginal region of bursal canal, immediately ventral to oviducal openings (Fig. 4A). Copulatory bursa saccate, situated immediately behind the pharyngeal pocket, occupying nearly three-quarters of dorso-ventral body space (Fig. 4B). Bursa lined with stratified, columnar vacuolated epithelium with basal nuclei; surrounding musculature absent. Bursal canal narrow, arising from mid-posterior wall of bursa, occupying nearly one-sixth of dorso-ventral body space, extending caudad to level of gonopore, then bending ventrally to enter common atrium. Bursal canal lining composed of cylindrical, infranucleated ciliated cells; musculature consisting of thin subepithelial longitudinal layer and thicker circular layer, latter particularly developed ventrally. Ectal reinforcement present, consisting of outer longitudinal musculature extending from atrium to about halfway along bursal canal. Testes well developed, dorsally situated, occupying about one-quarter of dorso-ventral body space, extending from level of posterior margin of ovaries to posterior end of body; abundant mature spermatozoa present. At level of posterior part of copulatory bursa and seminal vesicle, vasa deferentia expanded into spermiducal vesicles, filled with sperm. Penis bulb large, occupying nearly entire dorso-ventral body space. Sperm ducts running dorso-medially along both sides of penis bulb. Seminal vesicle strongly elongated, extending anteriorly to level of copulatory bursa or even below it (Figs 4C, 4D). In specimens ZMHNU-GTZ3, RMNH.VER.22786.1, ZMHNU-GTZ9, RMNH.VER.22786.2, and ZMHNU-GTZ12, seminal vesicle elongate and ventrally displaced, with anterior extension reaching level of posterior wall of copulatory bursa (Figs 4D, 5A). Seminal vesicle lined with flat nucleated epithelium and surrounded by thick layer of irregularly crosswise arranged, intermingled muscle fibres. In specimens with a ventrally displaced seminal vesicle (ZMHNU-GTZ3, RMNH.VER.22786.1, ZMHNU-GTZ9, RMNH.VER.22786.2, and ZMHNU-GTZ12) sperm ducts open symmetrically into mid-dorsal region of posterior part of seminal vesicle (Fig. 5A). In specimens in which the seminal vesicle is situated more dorsally, sperm ducts open into mid-ventral region of its posterior part (Fig. 6A). Posterior portion of seminal vesicle narrowing into long, slender duct, curving ventrad to connect with small, rather stubby diaphragm near ventral root of penis papilla (Figs 4E, 5A–B, 6A–B). This connecting duct is lined with nucleated epithelium and surrounded by thin circular musculature. Diaphragm receiving abundant secretion of orange-staining penis glands (Figs 4E, 5A–B), pointing into slender ejaculatory duct lined with cuboidal infranucleated epithelium (Fig. 4F). Ejaculatory duct curving postero-dorsally, opening subterminally through dorsal wall of penis papilla. Penis papilla strongly dorso-ventrally asymmetrical; dorsal lip greatly reduced, less than half length of ventral lip; ventral lip elongate, slender, curves dorsal at about 90 o angle, forming characteristic upward-curved structure (Figs. 4F, 5A–B, 6A). Penis papilla covered with nucleated epithelium, underlain by subepithelial circular muscles followed by longitudinal muscle fibres. Penis fold distinct, projecting from dorsal root of penis papilla into male atrium. Male atrium small; communication with common atrium rather wide. Common atrium leading to gonoduct opening ventrally through gonopore. Gonoduct lined with tall columnar, nucleated epithelium, receiving openings of abundant erythrophilic cement glands (Fig. 5A–B, 6A–B). 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.
Institutions: Henan Normal University, Naturalis Biodiversity Center
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: gold
OpenAlex ID: W7167224685
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