Dugesia parasagitta, 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 : 538-539

DUGESIA PARASAGITTA SLUYS & SOLÀ SP. NOV.

( FIG. 13 )

Material examined: Holotype: ZMA V.Pl. 7118.1, Ermones , Corfu, Greece, 39°36′37.98″N, 19°46′41.64″E, somewhat higher upstream than ZMA V.Pl. 7119, 20 April 2009, coll. R. Sluys , sagittal sections on 13 slides.

Paratypes: ZMA V. Pl. 7118.2, ibid., horizontal sections on eight slides; V.Pl. 7118.3, ibid., sagittal sections on six slides.

Other material examined: ZMA V. Pl. 7119.1, Ermones, Corfu, Greece, 39°36′41.93″N, 19°47′1.40″E, outflow of river into the sea, 20 April 2009, coll . R. Sluys , sagittal sections on five slides; V. Pl. 7119.3, ibid., horizontal sections on six slides ; V. Pl. 7119.4, ibid., sagittal sections on 18 slides , V. Pl. 7119.5, ibid., sagittal sections on 14 slides ; V. Pl. 7119.6, ibid., sagittal sections on 17 slides .

Etymology: The specific epithet is based on the prefix para (somewhat resembling, related to) and the specific epithet of the species D. sagitta .

Diagnosis: The species differs morphologically from its closest relative, D. sagitta , in the presence of a very large dorsal penial fold, very small ventral fold and a ventrally displaced ejaculatory duct.

Ecology and distribution: The species is known only from two sites in the same river. One site is close to the opening of this river into the sea, while the type locality is located slightly farther upstream.

Comparative discussion: The taxonomic status of D. sagitta ( Schmidt, 1861) from Corfu as a valid and separate species was clarified by De Vries (1984). Prior to her study, the Dugesia populations from Corfu were usually considered to be conspecific with D. gonocephala , following a conclusion reached by Komárek (1925). To avoid future taxonomic confusion, De Vries (1984) fortunately designated a series of neotypes for D. sagitta . Although the International Code of Zoological Nomenclature (ITZN, 1985; ICZN, 1999) restricts designation of a neotype to only one specimen that forms the new name-bearing type of a nominal species and thus does not allow it to be a series of animals, the neotype specimens specified by De Vries (1984: 104) represent a morphologically homogeneous set of animals. As neotype locality was chosen Messonghi River, just west of Messonghi.

The Ermones population was first mentioned by Ball (1979), who attributed it to D. gonocephala . In the same paper the karyotype of presumed D. gonocephala from Corfu was analysed but it is not clear which population was studied, either the one from Ermones or the animals from Messonghi River. However, De Vries (1984) writes that animals from the neotype locality of D. sagitta , i.e. Messonghi River, were analysed.

Our integrative analysis of the populations that we sampled from Corfu revealed an unexpected and interesting situation. Molecular analysis of both COI and ITS-1 grouped the various populations sampled into three clades (cf. Solà et al., 2013). These three clades are also identified as separate entities in the GMYC analysis ( Fig. 2 , entities 1, 2 and 3). One clade was formed by populations 27, 28, 29 and 30 (i.e. north of the San Salvador mountain range). The second clade consisted of populations 33 and 34. The third clade consisted of two samples from basically the same locality, namely Ermones (localities 31 and 32) ( Fig. S2 ).

On the basis of morphological analysis of the populations from Corfu we were able to differentiate between only two types. The majority of the populations sampled conformed to the classical diagnosis of D. sagitta , notably in the presence of a well-developed dorsal fold and a very small or absent ventral fold, and with a central ejaculatory duct. This also holds true for populations that we have not re-collected, but of which material is present in the collections of the NBC: Messonghi River, Marbella beach (now called Par. Ag. Ioannis Peristeron) and Mesaria. However, the population from Ermones (ZMA V.Pl. 7118 + V.Pl. 7119) is characterized by a very large dorsal penial fold, very small ventral fold and a ventrally displaced ejaculatory duct ( Fig. 13 ). Thus, coincidence of molecular and morphological results suggests that at least the population from Ermones is well differentiated from other populations on Corfu. Therefore, we do here describe this population as the new species D. parasagitta .

It remains remarkable that the populations that are geographically closest to the D. sagitta type locality, namely ZMA V.Pl. 7120 from near Vouniatades (locality 33) and ZMA V.Pl. 7121 from near Benitses (34) (entity 2, Fig. 2 ), differ molecularly so much from the populations in the northern part of the island (entity 1, Fig. 2 ), whereas morphologically they cannot be distinguished from each other, nor from the neotype population.

After the separation and description of D. parasagitta , the nominal species D. sagitta actually forms a paraphyletic taxon, according to all molecular analyses done so far (cf. Solà et al., 2013; COI gene tree, Fig. 2 ). Furthermore, the geographical distribution of the various populations ( Fig. S2 ) suggests that these two units form two independent lineages. In view of the definition of a species as an independently evolving lineage, this suggests that these lineages are actually two different species. We do take a conservative approach to taxonomy and do not assign formal species status to these taxa, pending the availability of further data. However, we do suggest that entity 2 (from localities 33 and 34, i.e. in the proximity of the neotype locality of D. sagitta ) is assigned to the nominal species D. sagitta , and that entity 1 (from localities 27 and 29) represents a UCS ( Fig. S2 , Table 1).

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 13. Dugesia parasagitta Sluys & Solà sp. nov. Photomicrograph of large dorsal penial fold in specimen ZMA V.Pl. 7118.1.