Dugesia naiadis, 2013

Sluys, Ronald, Solà, Eduard, Gritzalis, Konstantinos, Vila-Farré, Miquel, Mateos, Eduardo & Riutort, Marta, 2013, Integrative delineation of species of Mediterranean freshwater planarians (Platyhelminthes: Tricladida: Dugesiidae), Zoological Journal of the Linnean Society 169 (3), pp. 523-547 : 535-538

DUGESIA NAIADIS SLUYS SP. NOV.

( FIGS 10–12 )

Material examined: Holotype: ZMA V.Pl. 7117.1, 650 m before Kipouries (coming from Fita), Chios, Greece, 38°30′43.31″N, 25°59′55.06″E, 30 April 2010, coll. M. Vila-Farré, sagittal sections on 12 slides.

Paratype: ZMA V.Pl. 7117.2, ibid., sagittal sections on nine slides .

Etymology: The specific epithet is derived from the Latin naias, water nymph, and alludes to the small freshwater stream from which the specimens were collected.

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Diagnosis: Dugesia naiadis is characterized by: vasa deferentia that open into the proximal, anterior section of the seminal vesicle; a short diaphragm; an acentral, ventrally displaced ejaculatory duct, opening terminally at the tip of a blunt penis papilla; a broad zone of cyanophilic secretion in the dorsal section of the penis papilla; oviducts that open symmetrically into the most proximal section of the bursal canal; a bursal canal provided with many irregular pleats and folds, surrounded by a welldeveloped coat of circular muscle and a zone of mesenchymatic, erythrophil gland cells; hyperplasic ovaries; lack of testes.

Ecology and distribution: Specimens were collected from a small creek; the species is known only from the type locality.

Description: Preserved specimens with low triangular head and rounded auricles ( Fig. 10 ), measuring up to 11 mm in length and 2.5 mm in width. Dorsal body surface pale brown; ventral surface pale. A pair of eyes is present and somewhat smaller additional eyes are present also in the sectioned specimens.

Pharynx located in the middle of the body, measuring about 1/6th of the body length. The mouth opening is located at the posterior end of the pharyngeal pocket.

Testes are completely absent. The ovaries are hyperplasic: ovarian tissue fills the entire dorsoventral space over a distance of about 750 μm. The midpoint of the hyperplasic ovaries is located at about 1/4th the distance between the brain and the root of the pharynx.

The oviducts open separately and symmetrically into the most proximal section of the bursal canal, i.e. close to the point where the canal communicates with the atrium ( Fig. 11 ). Erythrophil shell glands discharge their secretion into the bursal canal, immediately ventrally to the oviducal openings.

The bursal canal is lined with a nucleated epithelium; it follows a somewhat undulating course towards the copulatory bursa, while giving rise to a number of irregular pleats or folds that project into the surrounding mesenchyme ( Fig. 12 ). The canal is surrounded by a very thin, subepithelial layer of longitudinal muscle, followed by a thick layer of circular muscle. Ectally to its surrounding coat of muscles the bursal canal is surrounded by a zone of mesenchymatic, erythrophil gland cells, which discharge their secretion into the lining epithelium of the canal. Only in specimen ZMA V.Pl. 7117.1 ( Fig. 12 ) could ectal reinforcement by some longitudinal muscles be detected on the posterior wall of the bursal canal, in the region of the oviducal openings.

In specimen ZMA V.Pl. 7117.1 ( Fig. 12 ) the copulatory bursa is a large sac-shaped structure that fills the entire dorso-ventral space, but in ZMA V.Pl. 7117.2 ( Fig. 11 ) the bursa is much smaller and also lined with cells with a more densely stained content.

Although the oviducts run from the level of the copulatory apparatus to the ovaries, vasa deferentia could be traced only in the vicinity of the penis bulb. After having penetrated the ventro-lateral wall of the penis bulb, the vasa deferentia open separately into the proximal, anterior section of the seminal vesicle. The latter gradually narrows towards a small diaphragm, through which it communicates with the ejaculatory duct. Seminal vesicle and ejaculatory duct are positioned in the ventral region of the penis papilla, which therefore is asymmetrical: its dorsal section is much larger that the ventral section. The ejaculatory duct receives the secretion of numerous erythrophil penis glands and opens terminally at the blunt tip of the penis papilla. The latter is a plugshaped structure that fills most of the male atrium. The penis papilla is covered with a nucleated epithelium that is underlain by a thin layer of circular muscle, followed by an equally thin layer of longitudinal muscle. The dorsal section of the penis papilla is traversed by a broad zone of strands of cyanophilic secretion that does not seem to open into the ejaculatory duct or through the covering epithelium of the papilla. The spaces present in the penial mesenchyme, near the tip of the papilla, seem to result from clefts in torn tissue.

Discussion

Presence of hyperplasic ovaries and complete absence of testes are signs that these animals probably concern sexualized specimens from an otherwise asexually reproducing population. Such sexualization may be induced either spontaneously (as was the case with these animals from Chios) or experimentally and has been reported for 11 species of Dugesia (cf. Charni et al., 2004 and references therein; Stocchino, Sluys & Manconi, 2012; Harrath et al., 2013). Furthermore, hyperplasic ovaries and poorly developed testes have been found also in ex-fissiparous specimens of Phagocata morgani ( Stevens & Boring, 1906; Benazzi & Ball, 1972).

The fortunate circumstance that animals of an otherwise asexually reproducing population sometimes develop reproductive organs enables taxonomic identification of such specimens. In that context, the animals from Chios should be compared with other species for which a ventrally displaced ejaculatory duct has been reported, forming a presumably monophyletic subset within the genus Dugesia ( Sluys et al., 1998) . This comparison should be restricted to those species in which the ventrally displaced ejaculatory duct opens terminally at the tip of the penis papilla, thus excluding species with a subterminal opening. This immediately excludes D. sicula , D. aethiopica Stocchino et al., 2013 and Dugesia arabica Harrath & Sluys, 2013 as candidate species because these have a subterminal opening of the ejaculatory duct. However, both D. aethiopica and D. arabica resemble the Chios specimens in the presence of a bursal canal with many elaborate folds, a feature that has been reported also for D. biblica (cf. Benazzi & Banchetti, 1972), albeit that in the latter it is much less developed in comparison with D. aethiopica , D. arabica and the Chios specimens of D. naiadis . For D. biblica Benazzi & Banchetti (1972) describe the bursal canal as having ‘... un diametro alquante irregolare...’ [a considerably irregular diameter], which agrees with our observations on specimens from Israel (ZMA V.Pl. 698.1, V.Pl. 699.1).

Another difference between the Chios animals and D. aethiopica and D. sicula concerns the openings of the oviducts into the bursal canal. In both D. sicula and D. arabica the oviducal openings are highly asymmetrical, in contrast to the symmetrical openings in D. naiadis (cf. Sluys, 2007 ; Harrath et al., 2013). In the specimens of D. aethiopica from Ethiopia the situation is different in that the oviducts open symmetrically into the ventral part of the horizontally running section of the bursal canal. In these type specimens the proximal section of the bursal canal approaches the atrium by running more or less parallel to the body surface, thus contrasting with the course of the canal in D. naiadis .

In the presence of mesenchymal glands around the bursal canal and the patch of cyanophilic secretion in the penis papilla D. naiadis resembles D. sicula , D. biblica and the presumed biblica specimens from Bucak, Turkey (ZMA V.Pl. 813). However, in other features D. naiadis differs from these taxa.

The phylogenetic analysis ( Fig. 1 ) shows that D. naiadis belongs to the sicula – aethiopica clade (as defined in Lázaro et al., 2009) with maximum support (100/1), being the sister group of D. aethiopica and D. sicula . The fact that the GMYC method ( Fig. 2 , Table 1, entity 33) delimits the four specimens of D. naiadis as a differentiated species supports the description of this new species. Interestingly, D. naiadis does not present the duplication in the nuclear ribosomal internal transcribed spacer-1 (ITS-1) molecule that D. aethiopica and D. sicula share (data not shown; cf. Baguñà et al., 1999; Lázaro et al., 2009).

On the basis of their gene identity we have been able to assign several asexual Dugesia populations from Chios to either D. naiadis or D. sicula (Table S5).

Figures

Figure 1. Bayesian tree inferred from the concatenated data set (COI + 18S). Labels correspond to species names. Node numbers correspond to bootstrap (ML)/posterior probability (BI); values are only indicated when>50/>0.80; ‘*’ indicates maximum support. The scale bar indicates substitutions per site.

Figure 2. Result of the GMYC analysis. Threshold-delimiting speciation and coalescent processes plotted as a broken line. Numbers indicate molecular-based entities; labels correspond to species names. Entities in green show correspondence between the molecular species delimitation method and the morphologically identified species. In orange are shown groupings where there is conflict between morphological and molecular methods. In blue are shown the groupings for which only molecular data are available.

Figure 10. Dugesia naiadis Sluys sp. nov. Dorsal view of preserved specimen.

Figures 11, 12. Dugesia naiadis Sluys sp. nov. 11. ZMA V.Pl. 7117.2. Sagittal reconstruction of the copulatory apparatus. 12. ZMA V.Pl. 7117.1. Sagittal reconstruction of the copulatory apparatus.