Dugesia umbonata Song & Wang, 2020
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publication ID |
https://dx.doi.org/10.3897/zse.96.52484 |
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publication LSID |
lsid:zoobank.org:pub:E6569135-C4D3-401F-947C-56D753ACEF67 |
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persistent identifier |
https://treatment.plazi.org/id/126FAA7D-9B17-42C8-BCFA-BF7AEF9FA9F6 |
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lsid:zoobank.org:act:126FAA7D-9B17-42C8-BCFA-BF7AEF9FA9F6 |
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scientific name |
Dugesia umbonata Song & Wang |
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sp. nov. |
Dugesia umbonata Song & Wang sp. nov.
Material examined. Holotype: PLA-0151 , Fengzui River , Chongqing, China, 29°05.29'N, 107°10.61'E, 8 February 2018, coll. Xiao-Zhou Hu, sagittal sections on 24 slides GoogleMaps .
Paratypes: PLA-0152 , ibid., sagittal sections on 28 slides ; PLA-0153 , ibid, horizontal sections on 8 slides ; PLA-0154 , ibid., transverse sections on 27 slides ; RMNH.VER.19968.a , ibid., sagittal sections on 18 slides ; RMNH.VER.19968.b , ibid., sagittal sections on 27 slides .
Habitat.
Specimens were collected from a shallow tributary of Fengzui River (29°05.29'N, 107°10.61'E), the latter located at the western side of Jinfo Mountain at an altitude of about 530 m above sea level (a.s.l.) (Fig. 2A View Figure 2 ). The Fengzui River is a tributary of Wujiang River, while the latter is a tributary of the Yangtse River (Fig. 2A View Figure 2 ). The animals were collected from the underside of small pebbles in the riverbed (Fig. 2B, C View Figure 2 ), which had a water depth of 3-10 cm; air temperature was about 9 oC. Only 15 specimens were collected at the beginning, none of which was sexually mature. After about 1.5 years of rearing under laboratory conditions, in total about 40 specimens eventually sexualised.
Diagnosis.
A blackish species of Dugesia characterised by the following characters: muscularised hump immediately antero-dorsally to a knee-shaped bend in its bursal canal; ejaculatory duct opening subterminally through the dorsal side of the penis papilla; oviducts opening asymmetrically into the female copulatory apparatus, with the right oviduct opening into the knee-shaped bend of the bursal canal and the left oviduct opening into the common atrium; an asymmetrical penis papilla; small diaphragm; presence of a duct between seminal vesicle and diaphragm.
Etymology.
The specific epithet is based on the Latin umbonis, rounded protuberance, and alludes to the muscularised hump that sits on the postero-dorsal portion of the bursal canal.
Description.
Fissiparous and ex-fissiparous animals exhibit similar external features, apart from body size. Description and measurements, presented below, are based on sexualised, ex-fissiparous specimens.
Living, sexualised ex-fissiparous specimens ranged from 1.93-3.14 cm in length and 1.97-3.44 mm in width (n = 5; Fig. 3A, B View Figure 3 ). A pair of eyes is located at about 1/21 of the body length as determined from the anterior body end (Figs 3A, B View Figure 3 , 4A View Figure 4 ). The distance between the eyes and the lateral body margin varies from 369-478 μm (n = 5), while the distance between the eye cups ranges from 129-297 μm (n = 5; Figs 3A, B View Figure 3 , 4A View Figure 4 ). Each eye cup contains numerous retinal cells. Auricular grooves are located near the body margins on either side of the head, at a position just posterior to the eyes (Figs 3A, B View Figure 3 , 4A View Figure 4 ).
The dorsal surface is blackish, the colouration being formed by dense accumulations of dark brown specks; the ventral surface is brown (Figs 3 View Figure 3 , 4 View Figure 4 ). Regions around the eyes and auricular grooves are unpigmented (Figs 3A, B View Figure 3 , 4A View Figure 4 ). A pale, narrow mid-dorsal stripe runs from anterior to the eyes to the tip of the tail; body margins are also pale (Figs 3A, B View Figure 3 , 4A View Figure 4 ).
The cylindrical pharynx is positioned at about 2/5-1/2 of the body length as determined from the anterior body margin (Fig. 3 View Figure 3 ); it measures about 1/10 of the total body length, i.e. about 2.26-3.01 mm in length and 129-297 μm in width (n = 5; Figs 3A, B View Figure 3 , 4C View Figure 4 ). The outer epithelium of the pharynx is underlain by a thick layer of longitudinal muscle, followed by 2-3 layers of circular muscle. The inner epithelium is underlain by a rather thick layer of circular muscles, followed by 2-3 layers of longitudinal muscle. The mouth opening is situated at the posterior end of the pharyngeal cavity (Fig. 4C View Figure 4 ).
A pair of hyperplasic ovaries is situated at a short distance behind the brain, i.e. at about 1/10-3/20 of the body length as determined from the anterior body margin (n = 5; Figs 3A, B View Figure 3 , 4B View Figure 4 ), the gonads measuring about 471-1049 μm in anterior-posterior direction and about 149-234 μm in width (n = 5; Figs 3A View Figure 3 , 4B View Figure 4 ).
The oviducts open asymmetrically into the female copulatory apparatus, with the right oviduct opening into the knee-shaped bend of the bursal canal, while the left oviduct opens into the common atrium (Figs 5E View Figure 5 , 6E View Figure 6 , 7E View Figure 7 ).
A large, elongated, sac-shaped copulatory bursa is situated posteriorly to the pharynx and is lined with a layer of vacuolated, nucleated cells (Figs 5 View Figure 5 - 7 View Figure 7 ). The bursal canal runs from the postero-dorsal wall of the copulatory bursa in a caudal direction to the left-side of the copulatory apparatus. Hereafter, the bursal canal makes a knee-shaped bend in the antero-ventral direction, after which it opens into the dorsal portion of the common atrium (Figs 5A, B, E View Figure 5 , 6A, E View Figure 6 , 7A, E View Figure 7 ). The bursal canal is lined by a nucleated, glandular epithelium, which is underlain by 2-3 layers of longitudinal muscles, followed by 6-8 layers of circular muscle. Shell glands discharge their cyanophilic secretion into the knee-shaped portion of the bursal canal (Figs 5B-D View Figure 5 , 6B-D View Figure 6 , 7B-D View Figure 7 ).
Immediately antero-dorsally to the knee-shaped bend, the bursal canal carries a voluminous, ellipsoidal muscular hump that measures about 428-475 μm in anterior-posterior direction and 268-292 μm in cross-section (n = 3; Figs 5A, E View Figure 5 , 6A, E View Figure 6 , 7A, E View Figure 7 ). The hump consists of irregular, nucleated mesenchymal cells and is surrounded by a coat of intermingled muscles; there are also muscle fibres traversing the hump in all directions in a more loosely arranged, irregular and reticulated way (Fig. 8 View Figure 8 ).
In none of the specimens examined, testes could be discerned. The penis consists of a plump, more or less barrel-shaped papilla and an elongated bulb, the latter consisting of intermingled longitudinal and circular muscle fibres (Figs 5B-D View Figure 5 , 6B-D View Figure 6 , 7B-D View Figure 7 ). The papilla is covered by a nucleated epithelium, which is underlain by 1-3 layers of circular muscles, followed by a layer of longitudinal muscle fibres.
The penis bulb houses an egg-shaped seminal vesicle, which is situated near the antero-ventral side of the penis bulb (Figs 5A, B, D, E View Figure 5 , 6B, D, E View Figure 6 , 7 View Figure 7 ). The seminal vesicle is lined with a nucleated epithelium and surrounded by a layer of longitudinal muscle. The vasa deferentia open separately through the antero-dorsal wall of the seminal vesicle.
At its dorsal portion, the seminal vesicle gives rise to an extension that initially is rather broad, but then quickly narrows, while following a postero-ventral course to the small diaphragm, through which it communicates with the ejaculatory duct (Figs 5B-E View Figure 5 , 6B-E View Figure 6 , 7B-E View Figure 7 ). The seminal vesicle and its extension are lined with a cuboidal, nucleated epithelium, which is underlain by 2-4 layers of circular muscle fibres. The small conical diaphragm is covered by an infranucleated epithelium that is underlain by 1-2 subepithelial layers of circular muscle. The diaphragm receives the abundant secretion of erythrophil penis glands, which discharge their secretion also into the most proximal, anterior portion of the ejaculatory duct (Figs 5B-E View Figure 5 , 6B-E View Figure 6 , 7 View Figure 7 ).
From the ventrally located diaphragm, the ejaculatory duct starts a postero-dorsally orientated course through the penis papilla, after a while exhibiting a dorsally directed knee-shaped bend, whereafter it opens subterminally through the dorsal side of the penis papilla, thus giving rise to an asymmetrical penis papilla (Figs 5B-E View Figure 5 , 6B-E View Figure 6 , 7B-E View Figure 7 ).
The male atrium is lined by an epithelium consisting of nucleated, cylindrical cells and it is surrounded by a subepithelial layer of circular muscle, followed by 2-3 layers of longitudinal muscle. The male atrium communicates with the common atrium via a pronounced constriction (Figs 5B, D, E View Figure 5 , 6B-E View Figure 6 , 7B-E View Figure 7 ). The common atrium is lined with a nucleated epithelium and is surrounded by a subepithelial layer of circular muscle, followed by a layer of longitudinal muscle. Abundant, erythrophilic cement glands discharge their secretion into the gonopore, gonoduct and the very ventral portion of the common atrium (Figs 5B, D, E View Figure 5 , 6B-E View Figure 6 , 7B-E View Figure 7 ). The gonopore is located at 1/3-1/4 (n = 5) of the body length, as determined from the posterior body margin (Fig. 4C View Figure 4 ).
Histochemical structure of the nervous system.
After histochemical reaction with AChE, the major nervous system appears as a copper-red, ladder-like structure, comprising a brain, two ventral nerve cords and accompanying lateral branches and transverse commissures (Fig. 9 View Figure 9 ). The brain is composed of the thickened anterior portions of the ventral nerve cords, thus forming the cerebral ganglia, which together form an inverted V-shaped or U-shaped brain, as the ganglia are connected by a commissure at their anterior ends (Fig. 9A, B View Figure 9 ). In addition, the ganglia communicate with each other by 6-7 thin, transverse commissures (n = 4; Fig. 9A, B View Figure 9 ). Each ganglion gives off 9-11 nerve branches (n = 4; Fig. 9A, B View Figure 9 ). The eyes lie at the lateral border of the cerebral ganglia (Fig. 9A, B View Figure 9 ). The two ventral nerve cords extend backwards from the posterior end of the cerebral ganglia and communicate at the tail end, giving off 43-47 lateral nerve branches on either side of the body (Fig. 9A, C View Figure 9 ), while there are 38-42 transverse commissures between the ventral nerve cords, which are especially numerous in the tail region (Fig. 9A, C View Figure 9 ). The lateral nerve branches communicate with the marginal or lateral nerve cords, which are only weakly developed (Fig. 9 View Figure 9 ).
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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