Dugesia gemmulata Sun & Wang, 2022

Liu, Yi, Song, Xiao-Yu, Sun, Zhong-Yin, Li, Wei-Xuan, Sluys, Ronald, Li, Shuang-Fei & Wang, An-Tai, 2022, Addition to the known diversity of Chinese freshwater planarians: integrative description of a new species of Dugesia Girard, 1850 (Platyhelminthes, Tricladida, Dugesiidae), Zoosystematics and Evolution 98 (2), pp. 233-243 : 233

publication ID	https://dx.doi.org/10.3897/zse.98.83184
publication LSID	lsid:zoobank.org:pub:E8B38FE7-A904-43D2-8024-EE0745E415C7
persistent identifier	https://treatment.plazi.org/id/4C439299-E70E-4421-98E9-6068C91A1423
taxon LSID	lsid:zoobank.org:act:4C439299-E70E-4421-98E9-6068C91A1423
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Dugesia gemmulata Sun & Wang
status	sp. nov.

Treatment

Dugesia gemmulata Sun & Wang sp. nov.

Material examined.

Holotype: IZCAS PLA-0101, a rural streamlet in Qingzhen City , Guizhou, China, 26°33.83'N, 106°13.65'E, 3 February 2018, coll. Zhong-Yin Sun, sagittal sections on 20 slides. GoogleMaps

Paratypes: IZCAS PLA-0102, ibid., sagittal sections on 30 slides; IZCAS PLA-0103, ibid., horizontal sections on 18 slides.

Habitat.

Specimens were collected from a rural streamlet (26°33.83'N, 106°13.65'E) at an altitude of about 1,400 m above sea level (a.s.l.) in Qingzhen City, Guizhou, China (Fig. 1A View Figure 1 ). The animals were collected from the underside of small pebbles in the riverbed (Fig. 1B, C View Figure 1 ), which had a water depth of 20-50 cm. Water temperature was about 19.9 °C, while air temperature was about 21.8 °C.

Diagnosis.

Dugesia gemmulata is characterised by the following characters: ventral part of the most posterior section of the bursal canal, just anteriorly to its point of communication with the common atrium, provided with a voluminous, ellipsoidal muscular swelling; sac- or egg-shaped seminal vesicle situated near the ventral body surface in anterior portion of the penis bulb; postero-dorsal wall of seminal vesicle communicates with a narrow duct that first runs almost vertically but then shows a postero-dorsally directed loop before connecting with a small diaphragm; ejaculatory duct opening terminally or subterminally; penis papilla asymmetrical, with dorsal lip provided with a bump; oviducts opening asymmetrically into female copulatory apparatus, with the left oviduct opening into the common atrium and the right oviduct opening into the vaginal section of the bursal canal.

Etymology.

The specific epithet is derived from the Latin gemmula, small bud, and alludes to the muscular swelling on the ventral wall of the bursal canal.

Description.

Body size of live, sexualised specimens ranged from 16.12 to 22.75 mm in length and 1.93 to 2.87 mm in width (n = 3; Fig. 3A, B View Figure 3 ), while asexual specimens ranged from 5.12 to 8.31 mm in length and 0.91 to 1.32 mm in width (n = 3). Sexualised and asexual individuals exhibited no differences in appearance, except for the body size. The following measurements are based on sexualised individuals. At a distance varying between 0.46 mm and 0.56 mm from the anterior body margin, two eyes are present in the middle of the low-triangular head, situated in pigment-free patches (n = 3; Fig. 3C View Figure 3 ). Each kidney-shaped eyecup contains numerous retinal cells. Unpigmented auricular grooves are marginally placed just posteriorly to the blunt auricles (Fig. 3C View Figure 3 ).

Dorsal body surface with a brown ground colour, overlain with scattered black pigmentation and provided with a thin, pale median line that runs from anterior to the eyes to the tail end (Fig. 3A-C View Figure 3 ); ventral surface much paler than dorsal surface (Fig. 3D View Figure 3 ).

The cylindrical pharynx lies more or less in the middle of the body and measures about 1/7 of the total body length, i.e., about 2.07-2.77 mm in length and 0.16-0.32 mm in width (n = 3; Fig. 3A View Figure 3 ). The entire pharynx is covered with a nucleated epithelium (Fig. 4B View Figure 4 ). The outer epithelium of the pharynx is underlain by 1-3 subepithelial layers of circular muscles, followed by a thin layer of longitudinal muscle fibres (Fig. 4B View Figure 4 ). The inner pharynx epithelium, which is densely ciliated, is underlain by a thin subepithelial layer of longitudinal muscle fibres, followed by 3-5 layers of circular muscles (Fig. 4B View Figure 4 ). The mouth opening is located at a distance of about 1/3-1/2 of the body length, as measured from the posterior body margin; the mouth is situated at the posterior end of the pharyngeal cavity (n = 3; Fig. 3B View Figure 3 ).

Testes could not be discerned. The large, elongated penis bulb consists of intermingled longitudinal and circular muscle fibres. The vasa deferentia open asymmetrically into the seminal vesicle, with the right vas deferens opening into the mid-anterior portion of the seminal vesicle in specimen PLA-0101 and into the mid-dorsal portion in specimen PLA-0102, while the left vas deferens opens into the postero-dorsal part of the seminal vesicle in specimen PLA-0101 and into the postero-ventral part in specimen PLA-0102 (Figs 4E View Figure 4 , 5C View Figure 5 ). The sac- or egg-shaped seminal vesicle is situated near the ventral surface in the anterior portion of the penis bulb; it is lined with a nucleated epithelium and surrounded by 1-2 layers of longitudinal muscles (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ). From the postero-dorsal wall of the seminal vesicle arises a narrow duct, lined with a glandular, nucleated epithelium and surrounded by 1-3 layers of circular muscle fibres, which first runs almost vertically but then shows a postero-dorsally directed loop before connecting with a small diaphragm (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ).

The very small diaphragm is lined by a nucleated epithelium, which is underlain by 1-2 layers of circular muscle and is pierced by the openings of erythrophil penial glands (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ). The diaphragm leads to a broad ejaculatory duct, which is lined by an infranucleated epithelium that is underlain with 1-3 layers of circular muscle fibres (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ).

The ejaculatory duct runs more or less centrally through the penis papilla and opens subterminally through the ventral wall of the penis papilla in specimens PLA-0101 and PLA-0103, while in specimen PLA-0102 the ejaculatory duct runs a ventrally displaced course and opens at the tip of the papilla (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ). The penis papilla is asymmetrical, in that its dorsal lip is larger than the ventral one, while the former carries a bump (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ). The papilla is covered by a thin, nucleated epithelium, which is underlain by a layer of longitudinal muscles, followed by 2-3 layers of circular muscles, the latter being thicker at the base of penis papilla (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ).

The ovaries are hyperplasic, with several scattered masses distributed in the body region directly posterior to the brain, filling up the entire dorso-ventral space (Fig. 4A View Figure 4 ). The left oviduct arises from the mid-lateral section of the ovary, while the right duct arises from a more antero-lateral section of the ovary (Fig. 4A View Figure 4 ). From the ovaries, the oviducts, which are lined with an infranucleated epithelium, run backwards and continue their course on either side of the pharyngeal pocket (Figs 4F View Figure 4 , 5D View Figure 5 ). Immediately posterior to the gonopore, the oviducts turn medially to open asymmetrically into the female copulatory apparatus, with the left oviduct opening into the common atrium and the right oviduct opening more dorsally into the vaginal section of the bursal canal (Figs 4E View Figure 4 , 5C View Figure 5 ).

The large, irregularly egg-shaped copulatory bursa is situated immediately anterior to the penis bulb and is surrounded by a thin layer of intermingled longitudinal and circular muscle fibres (Figs 4C-F View Figure 4 , 5 View Figure 5 ). The bursal canal arises from the posterior surface of the copulatory bursa and runs caudally to the left of the copulatory apparatus, subsequently communicating with the dorsal portion of the common atrium (Figs 4E, F View Figure 4 , 5C, D View Figure 5 ). The bursal canal is lined by a nucleated, glandular epithelium, which is underlain by a subepithelial layer of longitudinal muscle fibres, followed by 2-5 layers of circular fibres. The coat of circular fibres on the ventral side of the bursal canal varies from 3-5 layers, while that on the dorsal side is thinner, being 2-3 layers thick. Furthermore, the ventral part of the most posterior section of the bursal canal, just anteriorly to its point of communication with the common atrium, carries a voluminous, ellipsoidal muscular swelling that measures about 348-481 μm in anterior-posterior direction (n = 3; Figs 4D, F View Figure 4 , 5B, D View Figure 5 , 6 View Figure 6 ). The swelling consists of irregular, nucleated mesenchymal cells and is surrounded by a coat of intermingled muscles; there are also muscle fibres traversing the swelling in all directions in a more loosely arranged, irregular and reticulated way (Figs 4D, F View Figure 4 , 5B, D View Figure 5 , 6 View Figure 6 ).

The male atrium is lined by an epithelium consisting of nucleated, cylindrical cells and is surrounded by a subepithelial layer of circular muscles, followed by 1-2 layers of longitudinal muscles. The male atrium communicates with the common atrium via a pronounced constriction (Figs 4C-E View Figure 4 , 5A, C, D View Figure 5 ). The common atrium is lined with an infranucleated epithelium, which is underlain by 1-2 layers of circular muscle, followed by a layer of longitudinal muscle. The common atrium opens ventrally through the gonopore, which is located at 1/3-1/4 of the body length (n = 3), as determined from the posterior body margin (Figs 4E, F View Figure 4 , 5A, C, D View Figure 5 ).

Massive shell glands are distributed posteriorly to the common atrium and near the vaginal section of the bursal canal (Figs 4E View Figure 4 , 5A, C View Figure 5 ). Near its opening into the common atrium, the bursal canal receives the cyanophilic secretion of the shell glands (Figs 4E View Figure 4 , 5A, C View Figure 5 ). Erythrophilic cement glands open into the ventral portion of the common atrium and into the gonoduct (Figs 4C, E View Figure 4 , 5A, C View Figure 5 ).