Dugesia improvisa, 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 : 532-535

DUGESIA IMPROVISA SLUYS & SOLÀ SP. NOV.

( FIGS 6–9 )

Material examined: Holotype: ZMA V.Pl. 7116.1, Melanes , Naxos, Greece, 37°5′3.38″N, 25°26′59.40″E, alt. 199 m, 9 April 2009, coll. Eduardo Mateos & Eduard Solà, sagittal sections on nine slides.

Paratypes: ZMA V.Pl. 7116.2, ibid., sagittal sections on ten slides ; V.Pl. 7116.3, ibid., horizontal sections on four slides ; V.Pl. 7116.4, ibid., sagittal sections on eight slides .

200 µm pg ed od vd

Etymology: The specific epithet is derived from the Latin adjective improvisus, unexpected, and alludes to our surprise in finding a second and new species of Dugesia on such a small island as Naxos.

Diagnosis: Dugesia improvisa is characterized by: an acentral, ventrally displaced ejaculatory duct, opening at the tip of the penis papilla; a short diaphragm; ectal reinforcement being confined to the posterior wall of the ascending portion of the bursal canal; vasa deferentia separately opening into the anterior section of the seminal vesicle, at a point close to the diaphragm; broad zone of abundant penis glands traversing the penial papilla and opening into the ejaculatory duct.

Ecology and distribution: Specimens were collected from under stones in a small, shallow pool, receiving the outflow of water from a concrete pipe. The species is known only from this type locality.

Description: Preserved specimens up to about 12.5 × 3 mm. Triangular head with distinct, blunt auricles. Posterior end obtusely pointed. Dorsal surface pale brown, with the pigment arranged in a finely reticulated pattern and with a concentration of pigment following the outline of the pharyngeal pocket ( Fig. 6 ). Dorsal body margin and ventral surface pale. The two eyes are situated in conspicuous pigment-free patches.

The pharynx is located in the posterior half of the body and measures about 1/8th of the body length in preserved specimens. The mouth opening is located at the posterior end of the pharyngeal pocket.

The testes are located dorsally and extend from the level of the ovaries to the posterior end of the body.

The vasa deferentia penetrate the antero-lateral wall of the intrabulbar seminal vesicle; the ducts open separately into the vesicle at a position very close to the diaphragm ( Fig. 7 ). The intrabulbar seminal vesicle is lined with an epithelium, consisting of columnar cells, that is pierced by the numerous openings of penis glands, the latter producing a granular, erythrophil secretion. At the free end of the lining epithelium of the seminal vesicle this secretion projects into the lumen as relatively large, pear-shaped, granular drops. Through a short, stubby diaphragm the seminal vesicle opens into the proximal, funnelshaped section of the ejaculatory duct.

The diaphragm is short. The proximal funnelshaped section of the ejaculatory duct, immediately adjacent to the diaphragm, houses a sickle-shaped flap of tissue or secretion ( Figs 7–9 ). This flap seems to be attached to the rest of the diaphragm by only a minute piece of tissue. The lining epithelium of the flap is pierced by the openings of the erythrophil penis glands that open into the seminal vesicle and also penetrate the epithelium of the rest of the diaphragm. The flap was observed in all four specimens examined and its histology suggested true mesenchyme, surrounded by an epithelium.

The ejaculatory duct runs slightly acentrally, i.e. ventrally displaced, through the penis papilla, opening at its tip. The major portion of the ejaculatory duct receives the conspicuous, abundant and granular secretion of erythrophil penis glands, which are located outside of the penis.

The penis papilla is a broad, pointed or blunt cone. The papilla is covered with a nucleated epithelium and is underlain with a subepithelial layer of circular muscles, followed by a layer of longitudinal muscles. The penis bulb is well developed and muscular.

The small, paired ovaries are situated at about 1/3rd of the distance between the brain and the root of the pharynx and are positioned directly medially to the ventral nerve cords. The oviducts arise from the dorsal surface of the ovaries and run backwards immediately dorsally to the ventral nerve cords. At the level of the copulatory apparatus the oviducts curve dorsomedially to open separately into the most proximal, posterior, section of the bursal canal, i.e. close to the point where the duct communicates with the atrium. Erythrophil shell glands open into the bursal canal immediately ventrally to the openings of the oviducts.

The bursal canal is lined with a cuboidal, nucleated epithelium and is surrounded by a reversed musculature: a thin subepithelial layer of longitudinal muscle, followed by a thicker layer of circular muscle. Around the proximal, posterior, section of the bursal canal this circular muscle layer is rather thick, but it becomes gradually thinner towards the copulatory bursa. Ectal reinforcement of the bursal canal musculature is only present along the proximal section of the canal, i.e. from its opening into the atrium to about the point where the duct curves anteriad. However, this ectal reinforcement is only present as a single layer of longitudinal muscle along the posterior wall of the ascending portion of the bursal canal; it was not observed along the anterior wall of this part of the canal. The bursal canal communicates with a large, sac-shaped copulatory bursa, which occupies most of the dorso-ventral space of the body. In two specimens the bursa contained remnants of a sclerotic spermatophore.

Discussion

The presence of a peculiar flap of tissue on the diaphragm sets D. improvisa immediately apart from any of the known species of Dugesia . However, in specimens of other species of Dugesia a more or less crescent-shaped stretch of secretion may be present in precisely the same position, albeit less clearly attached to the epithelium, while in these specimens its staining properties clearly suggest a glandular origin. In these animals, and also in D. improvisa , this flap or stretch of secretion may be related to the formation of the spermatophore (which is formed in the ejaculatory duct) or to the transfer of sperm into the latter. However, in D. improvisa the flap did not resemble a spermatophore in statu nascendi but suggested true mesenchyme surrounded by an epithelium. We are hesitant to consider this feature as a diagnostic character of D. improvisa , but would first prefer to check the presence of this flap in another series of individuals of D. improvisa . Unfortunately, additional material is not presently available. However, D. improvisa also presents a combination of other characters that makes it different from its congeners.

In the fact that the vasa deferentia open into the seminal vesicle at a point close to the diaphragm, D. improvisa resembles a good number of other species of Dugesia (cf. Sluys et al., 1998, table II). However, in other features these species differ much from D. improvisa , for example in the presence of penial or atrial folds, except Dugesia subtentaculata ( Draparnaud, 1801) and D. burmaensis ( Kaburaki, 1918) . However, the atrium of D. subtentaculata shows a distinct musculo-glandular area (cf. De Vries, 1986), which is absent in D. improvisa . Furthermore, D. subtentaculata also possesses a ring of spongiose mesenchymatic tissue in the penis papilla that is absent in D. improvisa . In addition, in D. subtentaculata the ectal reinforcement along the bursal canal is much more developed and extends much farther anteriad.

The gross morphology of the copulatory apparatus of D. burmaensis is very similar to that of D. improvisa . However, for D. burmaensis it has been reported that the oviducts arise from the anterolateral wall of the ovaries, contrasting with their dorsal origin in D. improvisa . Dugesia burmaensis resembles D. improvisa in the presence of highly developed penis glands, discharging their abundant secretion into the ejaculatory duct. Such a broad zone with abundant secretion traversing the penis papilla is also characteristic of D. sagitta from Corfu. However, there are a number of clear differences between D. sagitta and D. improvisa .

In D. sagitta the penis papilla is blunt and provided with distinct, asymmetric penial folds at both the dorsal and the ventral side of its base (cf. De Vries, 1984), which are absent in D. improvisa . Furthermore, in D. sagitta the ejaculatory duct follows a central course through the penis papilla, whereas it has a ventrally displaced trajectory in D. improvisa . In addition, the ectal reinforcement of the bursal canal extends much farther anterior in D. sagitta .

In all molecular analyses D. improvisa is the sister species of D. ariadnae ( Fig. 2 ; Solà et al., 2013), the latter also restricted in its distribution to the island of Naxos. However, the two species are clearly delimited in the GMYC analysis, while morphologically D. ariadnae is very different from D. improvisa . In particular, D. ariadnae is characterized by two welldeveloped adenodactyls that are suspended from the dorsal atrial wall, one on either side of the base of the penis. On the basis of our comparative and integrative analysis, as presented above, we conclude that D. improvisa concerns a new species.

Figures

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 6. Dugesia improvisa Sluys & Solà sp. nov. Dorsal view of preserved specimen.

Figures 7, 8. Dugesia improvisa Sluys & Solà sp. nov. 7. ZMA V.Pl. 7116.2. Sagittal reconstruction of the copulatory apparatus. 8. ZMA V.Pl. 7116.1. Sagittal reconstruction of the copulatory apparatus.

Figure 9. Dugesia improvisa Sluys & Solà sp. nov. Photomicrograph of penial complex of specimen ZMA V.Pl. 7116.4, showing the sickle-shaped flap of tissue or secretion.