Dugesia Girard, 1850

Dols-Serrate, Daniel, Stocchino, Giacinta Angela, Nuin-Villabona, Paula, Sluys, Ronald & Riutort, Marta, 2024, New insights into the evolution and biogeography of freshwater planarians on islands in the Tyrrhenian Sea, Western Mediterranean Basin, with the integrative description of a new endemic species from Corsica (Platyhelminthes: Tricladida: Dugesia), Zoological Journal of the Linnean Society 201 (4), pp. 1-16 : 8-11

publication ID	https://doi.org/ 10.1093/zoolinnean/zlae080
publication LSID	lsid:zoobank.org:pub:28E25DD-AB1D-4DAD-888F-9534690EBD4C
DOI	https://doi.org/10.5281/zenodo.13769852
persistent identifier	https://treatment.plazi.org/id/2E7B87D4-4D62-A513-FED9-F8F4FEC972A1
treatment provided by	Plazi
scientific name	Dugesia Girard, 1850
status

Treatment

Genus Dugesia Girard, 1850 View in CoL

Dugesia xeropotamica Stocchino, Dols-Serrate & Riutort , sp. nov.

Material examined: Individuals CA1291-08 , CA1291-09 , CA1291-11 , and CA1291-13 from locality 19 and MG1292- 08 , MG1292-09 , and MG1292-13 from locality 20 were analysed molecularly; corresponding GenBank accession numbers are detailed in Supporting Information , Table S1 View Table 1 . Holotype: RMNH.VER.21534.1, Seccu River, locality Montegrosso (42°32 ʹ 17.4″ N, 8°50 ʹ 38.5″ E), Corsica, 29 November 2019, coll. D. Dols-Serrate, L. Leria, one set of sagittal sections on nine slides. Paratype: CGAS Pla 29.1, ibid., sagittal sections on seven slides GoogleMaps .

Diagnosis: Molecularly, D. xeropotamica comprises individuals that are identified as a single evolutionary unit alongside individuals from localities 19 and 20 of the present work when using a multispecies coalescent-based method, such as BPP, with the loci and settings detailed in the Materials and Methods section of the present paper, or equivalent molecular species delimitation analyses.

Morphologically, D. xeropotamica is characterized by the presence of the following features: short, more or less barrel-shaped, and asymmetrical penis papilla; dorsal lip of the penis papilla bigger than the ventral one; ventrally displaced ejaculatory duct, opening terminally at tip of the penis papilla; short ejaculatory duct; large, conical diaphragm; symmetrical openings of the vasa deferentia into the posterior section of the seminal vesicle, i.e., close to the diaphragm; oviducts opening symmetrically into the vaginal portion of the bursal canal; ectal reinforcement musculature on bursal canal extending from vaginal region almost up to the copulatory bursa; numerous extrabulbar penial glands.

Etymology: The specific epithet is derived from the Greek words ‘ξεΡός’(xeros), meaning ‘arid’, and ‘ποταμός’(potamos), meaning ‘river’. The epithet alludes to the name of the type locality Seccu River, whose Corsican name translates to ‘Arid River’. This river runs dry during the summer season, and its course disappears as it approaches the sea.

Geographical distribution: This species is known only from the type locality, Seccu River (Montegrosso, locality 20 in Fig. 1 View Figure 1 ), Haute-Corse, Corsica , and from a small stream running parallel to the Figarella River , known as Lioli Rivulet (Calvi, locality 19 in Fig. 1 View Figure 1 ), Haute-Corse, Corsica .

Reproduction: Sexual.

Description: Two eyes are present in the centre of the low triangular head. Dorsal surface brown with two longitudinal dark brown stripes on either side of the body ( Fig. 4 View Figure 4 ); ventral surface pale. Unfortunately, it was not possible to take photographs of live animals in the field, and the head was removed for DNA extraction.

Inner and outer pharyngeal musculature bilayered, i.e., without an extra, third, outer longitudinal muscle layer in the inner sheath of muscles. The mouth opening is situated at the hind end of the pharyngeal pocket.

The infranucleated oviducts run ventrally in a caudal direction to the level of the genital pore, whereafter they open separately and symmetrically into the vaginal portion of the bursal canal.

The numerous testes are situated dorsally on either side of the body and extend to almost the posterior end of the body. Vitellaria are located between the testes and the intestinal branches.

The large, more or less cuboidal copulatory bursa occupies the entire dorsoventral space; it is lined by a columnar, vacuolated, and glandular epithelium with basal nuclei and is surrounded by a layer of muscles. From the posterodorsal wall of the bursa, the bursal canal runs in a caudal direction to the left side of the copulatory apparatus and then, at the level of the gonopore, exhibits a knee-shaped bend, whereafter it opens through the roof of the genital atrium. The bursal canal is lined with cylindrical, infranucleated, ciliated cells and is surrounded by a thin subepithelial layer of longitudinal muscles, followed by a layer of circular muscle. Ectal reinforcement musculature is present in the form of a well-developed layer of longitudinal muscles running ectally to the circular layer around the bursal canal, extending from the opening of the bursal canal into the atrium to the copulatory bursa ( Figs 5A View Figure 5 , 6A View Figure 6 ). Shell glands discharge their erythrophil secretion into the vaginal region of the bursal canal, at the level of the oviducal openings ( Fig. 5 View Figure 5 ).

The moderately developed penis bulb consists of intermingled longitudinal and circular muscle fibres. The penis bulb houses a spacious seminal vesicle, which is lined with a pleated epithelium. Numerous extrabulbar penial glands penetrate the anterior wall of the penis bulb to discharge their secretion into the proximal tract of the ejaculatory duct ( Figs 5 View Figure 5 , 6B View Figure 6 ).

At the level of the penis bulb, the vasa deferentia curve dorsomedially and then penetrate the latero-anterior wall of the bulb to open separately and symmetrically into the posterior portion of the seminal vesicle, close to the diaphragm. In specimen RMNH.VER.21534.1, the vasa deferentia are swollen to form spermiducal vesicles.

The stubby and asymmetrical penis papilla is characterized by a dorsal lip that is bigger than the ventral one. In specimen RMNH.VER.21534.1, the dorsal lip is also much longer than the ventral one ( Fig. 5 View Figure 5 ). The seminal vesicle opens into the ejaculatory duct via a well-developed conical diaphragm. The penis papilla is covered by an infranucleated epithelium, which is underlain by a subepithelial layer of circular muscles. The ejaculatory duct is rather short, measuring about one-half of the length of the penis papilla; it follows a ventral course through the papilla and has a terminal opening at its blunt tip. The ejaculatory duct contained an empty spermatophore in the two specimens examined and is lined by a cuboidal, infranucleated epithelium and surrounded by a subepithelial layer of longitudinal muscles ( Fig. 5 View Figure 5 ).

The genital atrium is lined by an infranucleated, columnar epithelium, which is underlain by a subepithelial layer of circular muscle, followed by a layer of longitudinal muscle fibres. The genital atrium opens to the exterior via the ventral gonopore. No cement glands were discerned in either of the specimens examined ( Fig. 5 View Figure 5 ).

Comparative discussion: In addition to its genetic differentiation from the rest of the species analysed in the present work, D. xeropotamica differs from its congeners in a unique combination of morphological characters concerning the copulatory apparatus. Notably, this concerns the following characters: short and asymmetrical penis papilla, with its dorsal lip being bigger than the ventral one; a ventrally displaced ejaculatory duct with its terminal opening; a large, conical diaphragm; symmetrical openings of the vasa deferentia into the seminal vesicle close to the diaphragm; presence of ectal reinforcement along the entire length of the bursal canal; symmetrical openings of the oviducts into the vaginal portion of the bursal canal; and numerous extrabulbar penial glands.

From the island of Corsica, thus far only two species of the genus Dugesia have been reported, i.e., D. benazzii and D. mariae , although the presence of D. benazzii must be evaluated as doubtful, according to a recent study (cf. Dols-Serrate et al. 2024). Dugesia xeropotamica shares with D. benazzii and D. mariae only the presence of a large, conical diaphragm, whereas it differs from these two species in the absence of a penial fold and the presence of numerous extrabulbar glands. Dugesia xeropotamica shares with D. mariae the ventral course of the ejaculatory duct and the extension of the ectal reinforcement up to the copulatory bursa ( Dols-Serrate et al. 2024).

The stubby, more or less barrel-shaped penis papilla of D. xeropotamica resembles that of D. leporii from Sardinia ( Pala et al. 2000). However, it differs from the latter species in the absence of a penial valve, the presence of a short ejaculatory duct, and presence of extrabulbar penial glands.

In its peculiar shape of the penis papilla, with its dorsal lip being longer than the ventral one, specimen RMNH.VER.21534.1 of D. xeropotamica resembles Dugesia japonica Ichikawa & Kawakatsu, 1964 from Matsumoto City (Honshû, Japan) and Dugesia ryukyuensis Kawakatsu, 1976 ( Ichikawa and Kawakatsu 1964, Kawakatsu et al. 1976). However, D. xeropotamica has a large, pointed diaphragm, in contrast to the small diaphragm present in the two above-mentioned Oriental species. Moreover, D. japonica and D. ryukyuensis have their openings of vasa deferentia located at the anterior section of the seminal vesicle, whereas in D. xeropotamica the sperm ducts open close to the diaphragm.

Extrabulbar penial glands are not rare in Dugesia and have been reported for a number of species, such as: Dugesia annandalei ( Kaburaki, 1918) , Dugesia andamanensis ( Kaburaki, 1925) , Dugesia mirabilis de Vries, 1988 , Dugesia debeauchampi de Vries, 1988 , Dugesia myopa de Vries, 1988 , Dugesia neumanni (Neppi, 1904) , Dugesia milloti de Beauchamp, 1952 , Dugesia monomyoda Marcus, 1953 , Dugesia bifida Stocchino & Sluys, 2014 , Dugesia burmaensis ( Kaburaki, 1925) , and Dugesia sigmoides Stocchino & Sluys, 2017 ( Kaburaki, 1918, 1925; Marcus, 1953; de Vries, 1988; Stocchino et al. 2014, 2017). Although extrabulbar glands are not explicitly reported in the literature on several other species, some of the drawings in the related descriptions, however, do suggest the presence of such glands. This is the case, for example, in accounts on Dugesia deharvengi Kawakatsu & Mitchell, 1989 ( Kawakatsu and Mitchell 1989: fig. 3A), Dugesia indica Kawakatsu, 1969 ( Kawakatsu 1969: fig. 2), Dugesia lanzai Banchetti & Del Papa, 1971 ( Sluys 2007: fig 9), Dugesia leclerci Kawakatsu & Mitchell, 1995 ( Kawakatsu and Mitchell 1995: fig. 10A), and Dugesia uenorum Kawakatsu & Mitchell, 1995 ( Kawakatsu and Mitchell 1995: fig. 6).

Absence of cement glands in D. xeropotamica appears to be peculiar among species of Dugesia , and even in triclads in general, because it is the secretion of these glands that allows cocoons to be fastened to the substratum ( Hyman 1951, Corso et al. 2006, Stocchino et al. 2014).