taxonID	type	description	language	source
35B9C03B44245392A6F69A46B4149A49.taxon	description	Figs 1, 2, 7, 8, 9	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
35B9C03B44245392A6F69A46B4149A49.taxon	diagnosis	Diagnosis. Dugesia aconcinna is characterised by the presence of the following features: live, mature animals rather small; asymmetrical openings of the oviducts into the common atrium; vasa deferentia separately opening into the posterior portion of the seminal vesicle; penis papilla of a very characteristic shape, with the part housing the connecting duct, diaphragm, and ejaculatory duct being a cylindrical structure with a blunt tip, while at its right-hand side sits a large penial fold that attaches to the base of the penis papilla; ejaculatory duct following a ventrally displaced course through the penis papilla, after which it opens at the tip of the papilla; presence of a duct between diaphragm and seminal vesicle.	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
35B9C03B44245392A6F69A46B4149A49.taxon	description	Description. Body of both asexual and sexual live specimens is quite small, with the sexual worms being only 6 – 9 mm in length and 1.0 – 1.2 mm in width. The low-triangular head is provided with two blunt auricles and two eyes, which are placed in pigment-free spots. Each pigmented eyecup houses numerous photoreceptor cells. The dorsal surface is yellow-brown, with many brown pigment granules and pale blotches all over the dorsal surface; the ventral surface is paler than the dorsal body surface (Fig. 7 C). Pharynx situated in the mid-region of the body, measuring ~ 1 / 6 of the body length. Mouth opening located at the posterior end of the pharyngeal pocket. Outer pharyngeal musculature is composed of a thin, subepithelial layer of longitudinal muscles, followed by a thin layer of circular muscles; no extra inner layer of longitudinal muscles was observed. The inner pharyngeal musculature consists of a thick, subepithelial layer of circular muscle, followed by a thin layer of longitudinal muscle. In those specimens in which we were able to examine the ovaries, most of the gonads were not hyperplasic (specimens TPYC 3, 5, 7, 8, and RMNH. VER. 22250.1), excepting specimens TPYC 6, and 11, and RMNH. VER. 22250.2. In general, the oval ovaries are situated at 1 / 3 – 1 / 4 of the distance between the brain and the root of the pharynx, occupying ~ 1 / 4 of the dorso-ventral space. The oviducts arise from the dorsal wall of the ovaries, then turn to the ventral side and run in a caudal direction to the level of the genital pore. Subsequently, the left oviduct bends dorsally to open into the common atrium, while the right oviduct exhibits a much more pronounced curvature towards the dorsal body surface, after which it recurves in antero-ventral direction to open into the most ventral, proximal portion of the bursal canal, at the point where the latter communicates with the common atrium (Figs 8 A, 9 A). Thus, the right oviducal branch opens dorsally to the left one. The oviducts are lined with a columnar, infranucleated epithelium. The sac-shaped copulatory bursa lies immediately behind the pharyngeal pocket and may occupy the entire dorso-ventral space or, at least, a considerable portion of it. The bursa is lined with a columnar, vacuolated epithelium with basal nuclei and is devoid of any surrounding musculature (Figs 8 B – D, F, 9). Near its communication with the postero-dorsal section of the bursa, the bursal canal is rather narrow and may occupy ~ 1 / 8 of the dorso-ventral space (Figs 8 F, 9 A). From thereon, the canal expands somewhat in diameter while it runs in a caudal direction to the left side of the male copulatory apparatus. At the level of the gonopore, the posterior section of the canal exhibits a rather abrupt, ventrally directed bend, after which it opens into the common atrium (Fig. 9 A). The bursal canal is lined with cylindrical, infranucleated, ciliated cells and is surrounded by a subepithelial layer of longitudinal muscles, followed by a layer of circular muscle; an extra outer layer of longitudinal musculature, forming the ectal reinforcement, extends from the copulatory bursa to the atrium. Erythrophil shell glands open into the vaginal region of the bursal canal, near the oviducal openings. The numerous, well-developed testes are situated dorsally and provided with mature spermatozoa. On either side of the midline of the body, testicular follicles are arranged in eight or nine longitudinal zones and extend from the posterior level of the ovaries to almost the posterior end of the body. At the level of the pharyngeal pocket, the vasa deferentia expand to form spermiducal vesicles, which are packed with mature spermatozoa (Fig. 9). Upon reaching the large penis bulb, the vasa deferentia turn dorso-medially and quickly decrease very much in diameter while penetrating the wall of the bulb. Subsequently, the sperm ducts open separately and symmetrically into the mid-posterior section of the seminal vesicle, near the point where it communicates with the connecting duct that leads to the diaphragm. The sperm ducts are lined with a nucleated epithelium and surrounded by a layer of circular muscle. The voluminous, oval seminal vesicle is lined by a flat, nucleated epithelium and is surrounded by a layer of intermingled muscle fibres. The seminal vesicle occupies ~ 2 / 5 of the dorso-ventral space and is located in the ventral portion of the penis bulb, close to the ventral body surface (Figs 8 B – D, 9). Although the penis bulb is rather shallow, it is, nevertheless, a large structure, occupying almost the entire dorso-ventral space (Figs 8 B – D, 9). A relatively long and broad duct connects the seminal vesicle with a small diaphragm, the latter leading to the ejaculatory duct (Figs 8 C, D, 9). This interconnecting duct is lined by an infranucleated epithelium and is surrounded by a layer of intermingled muscle fibres. The small diaphragm is located at the level of the root of the penis papilla and receives the abundant secretion of erythrophil penis glands (Figs 8 C, D, 9). Both the connecting duct and the ejaculatory duct run a ventrally displaced course through the penis papilla, with the relatively broad ejaculatory duct opening at the tip of the papilla (Figs 8 D, F, 9). The ejaculatory duct is lined with a cuboidal, infranucleated epithelium and is devoid of any surrounding musculature. The penis papilla has a very characteristic shape. The part that houses the connecting duct, diaphragm, and ejaculatory duct is a cylindrical structure with a blunt tip. This seems to be a rather symmetrical portion of the papilla but it should be noted that it concerns a lateral, left-hand part of the penis papilla. The right-hand part of the papilla develops a large penial fold (Figs 8 E, 9 B) that attaches to the base of the penis papilla. Penis papilla and penial fold are covered with a nucleated epithelium, which is underlain by a subepithelial layer of circular muscle, followed by a layer of longitudinal muscle fibres (Figs 8 B – F, 9). The genital atrium is divided into a common atrium and male atrium. The common atrium communicates with a gonoduct, which leads to the ventral gonopore; the gonoduct is lined by a columnar epithelium and receives the openings of cement glands (Fig. 9).	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
35B9C03B44245392A6F69A46B4149A49.taxon	etymology	Etymology. The specific epithet is derived from the Latin adjective aconcinna, asymmetrical, and alludes to the asymmetrical penial fold as well as the asymmetrical oviducal openings into the bursal canal.	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
35B9C03B44245392A6F69A46B4149A49.taxon	discussion	Discussion. A good number of Dugesia species possesses so-called penial annexes in the form of penial folds, which sometimes were indicated by the term adenodactyl. However, the term adenodactyl should not be applied to these penial annexes (Stocchino et al. 2017). Penial folds are located at the base of the penial papilla and are usually covered by the musculature of the penis bulb; folds may be of the parenchymatic-muscular type or of the parenchymatic-musculo-glandular type (Stocchino et al. 2017). Furthermore, penial folds may be located at both the ventral and dorsal side of the penis papilla, albeit the ventral fold may be smaller than the dorsal one, or a single fold may be restricted to the dorsal, dorso-lateral, or lateral portion of the papilla. Such a single fold is present in ~ 20 species of Dugesia. For the present comparative discussion, it suffices to concentrate on those species that exhibit a dorso-lateral or lateral penial fold more or less comparable to that of D. aconcinna, viz., D. arcadia de Vries, 1988, D. benazzii Lepori, 1951, D. golanica Bromley & Benazzi, 1991, D. hoidi Dols-Serrate, Stocchino & Riutort, 2024, D. iranica Livanov, 1951, D. libanica Bromley & Benazzi, 1991, D. mariae Stocchino, Dols-Serrate & Riutort, 2023, D. minotauros de Vries, 1984. However, all of these species differ from D. aconcinna in the absence of a connecting duct between the seminal vesicle and the diaphragm, perhaps excepting D. izuensis Katô, 1943 (cf. Sluys et al. 1998: table II; Dols-Serrate et al. 2024). For D. izuensis a diaphragm was not described but it is presumed that the abundant openings of eosinophilic penial glands approximately halfway into the ejaculatory duct (Kato 1950; Kawakatsu 1983) coincides with the location of the diaphragm, which is presumably very small. However, in other aspects D. izuensis is rather different from D. aconcinna. For example, in D. izuensis the penis papilla is a massive and plump structure, whereas the papilla in D. aconcinna is cylindrical. Other differences concern the penial fold. In D. izuensis the fold has the shape of a conical papilla with the central part filled with cyanophilic secretion, in contrast to the flap-like fold of D. aconcinna that lacks any secretions. With respect to the shape and position of its penial fold, D. aconcinna resembles D. benazzii, D. hoidi, and D. mariae, all of which possess a flap-like penial fold that extends dorso-laterally of the penis papilla, which holds true also for D. minotauros (de Vries 1984; Dols-Serrate et al. 2024). However, in all of these species the fold is situated on the left side of the penis papilla, in contrast to D. aconcinna in which the fold extends over the right side of the papilla. But there are also other differences. In D. benazzii and D. hoidi, the two vasa deferentia follow highly asymmetrical trajectories before opening, equally asymmetrically, into the seminal vesicle. In contrast, in both D. mariae and D. aconcinna the sperm ducts follow symmetrical trajectories. In D. iranica the penial fold sits also on the left side of the penis papilla, albeit it is not a flap-like fold, but a conical structure of variable size, which sometimes may be as large as the penis papilla; it is of the musculo-glandular type. All of this is different from the situation in D. aconcinna. Similarly to D. aconcinna, D. libanica possesses also a relatively long, cylindrical penis papilla with a blunt tip, with at its right-hand side a well-developed penial fold. In contrast to D. aconcinna, the fold of D. libanica is not flap-like but consists of a pear-shaped papilla, located dorsally to the right of the penis papilla, that may reach a length of ~ 3 / 4 of the penial papilla (Bromley and Benazzii 1991). Notably, none of above-mentioned species belongs to the same clade as D. aconcinna. Although, these species (D. adunca, D. ancoraria, D. bengalensis, and D. notogaea) are closely related molecularly, they can be easily distinguished from D. aconcinna by anatomical features.	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
6A0099F70FD45834BE0B3762F9816AF2.taxon	description	Figs 1, 2, 3, 4, 5, 6	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
6A0099F70FD45834BE0B3762F9816AF2.taxon	diagnosis	Diagnosis. Dugesia saccata is characterised by the presence of the following features: symmetrical openings of the oviducts into the most proximal section of the bursal canal, near the point where the latter communicates with the atrium; a sac-shaped expansion at the knee-shaped bend of bursal canal; vasa deferentia opening symmetrically into posterior portion of the seminal vesicle; ventrally displaced ejaculatory duct with subterminal opening; a duct between diaphragm and seminal vesicle; mixoploid karyotype, with diploid chromosome portraits of 2 n = 2 x = 14, and triploid complements of 2 n = 3 x = 21, with all chromosomes being metacentric.	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
6A0099F70FD45834BE0B3762F9816AF2.taxon	etymology	Etymology. The specific epithet is derived from the Latin noun saccus, bag, and alludes to the sac-shaped expansion at the knee-shaped bend of the bursal canal.	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
6A0099F70FD45834BE0B3762F9816AF2.taxon	discussion	Discussion. There is one character that immediately sets D. saccata apart from all of its known congeners, the sac-shaped expansion on the posterior section of the bursal canal, near the knee-shaped bend of the canal. This is slightly reminiscent of a situation in Dugesia aethiopica Stocchino, Corso, Manconi & Pala, 2002, in which the posterior section of the bursal canal, immediately before receiving the separate openings of the oviducts, is expanded in lateral direction and gives rise to several large folds (Sluys 2007). However, this is merely a superficial resemblance to the situation in D. saccata, and these two species also differ in many other features. For example, D. aethiopica shows a horizontal approach of the bursal canal to the atrium, which represents a rare feature among species of Dugesia and is also absent in D. saccata. In Dugesia arabica Harrath & Sluys, 2013 the bursal canal is considerably expanded as well as highly folded in the region of the oviducal openings (Harrath et al. 2013). However, this situation differs from that in D. saccata in that the expansion sits near the oviducal openings, whereas in D. saccata the sac-shaped expansion occurs dorsally, or entally to the openings of the oviducts into the bursal canal. Another difference between these two species concerns the presence of a duct between seminal vesicle and diaphragm in D. saccata and absence of such a duct in D. arabica. Two characteristic features of D. saccata may be found also in other species of Dugesia, a ventrally displaced ejaculatory duct with subterminal opening and the presence of a duct between the seminal vesicle and the diaphragm. Besides D. saccata, these two character states are also expressed, among others, in the three Chinese species D. majuscula, D. umbonata Song & Wang, 2020, and D. verrucula Chen & Dong, 2021 (Song et al. 2020; Wang et al. 2021 a, b). However, in contrast to D. saccata, in both D. majuscula and D. umbonata the ejaculatory duct has a subterminal dorsal opening at the tip of the penis papilla, while D. verrucula exhibits a permanent dorsal bump near the root of the penis papilla, which is absent in D. saccata. Another difference concerns the presence of a large muscularised hump on the dorsal surface of the bursal canal of D. umbonata, which is absent in D. saccata. Although these three species (D. umbonata, D. verrucula, and D. saccata) belong to the same clade, they are molecularly well-differentiated. On the other hand, while D. saccata, D. pendula, D. tumida, and D. majuscula belong to the same small clade, they are anatomically well differentiated. In Dugesia species, the basic chromosome number concerns three types, 7, 8, and 9. Previous studies have shown that in China number 8 is the most frequent type, while 7 is much rarer (Wang et al. 2024). In that respect, it is noteworthy that the basic chromosome number in D. saccata is n = 7, which is shared only with D. pendula, D. hepta Pala, Casu, & Vacca, 1981, D. batuensis Ball, 1970, and D. ryukyuensis Kawakatsu, 1976 (Kawakatsu et al. 1976; Pala et al. 1981; Khang et al. 2017; Wang et al. 2024). However, D. pendula exhibits an aneuploid plus mixoploid karyotype, with diploid (2 n = 2 x = 14 + 0 - 1 B-chromosome) and triploid (2 n = 3 x = 21 + 0 - 1 B-chromosome) sets, while D. batuensis exhibits six metacentric chromosomes and one subtelocentric chromosome, and D. ryukyuensis shows six metacentric chromosomes and one submetacentric chromosome, which is the case also in D. hepta. In contrast, D. saccata exhibits a mixoploid karyotype with diploid (2 n = 2 x = 14) and triploid (2 n = 3 x = 21) sets, with all chromosomes being metacentric, thus contrasting with the chromosome complements of the other species. In fact, D. saccata produced infertile cocoons and only showed asexual reproduction by means of fission, which corresponds with its poorly developed or hyperplasic ovaries and the triploid chromosome complement. It has been established that in such abnormal ovaries the oocytes are anomalous, thus preventing regular oogenesis (Harrath et al. 2014).	en	Wang, Lei, Chang, Yi-Fang, Sun, Xin-Xin, Sluys, Ronald, Liu, De-Zeng, Dong, Zi-Mei, Chen, Guang-Wen (2025): Two new species of freshwater planarian from Hainan Island and Leizhou Peninsula, southern China (Platyhelminthes, Tricladida, Dugesiidae). ZooKeys 1233: 289-313, DOI: 10.3897/zookeys.1233.142976
