Polycelis nigra (Müller, 1774), Muller, 1774

Vila-Farré, Miquel, Sluys, Ronald, Almagro, Ío, Handberg-Thorsager, Mette & Romero, Rafael, 2011, Freshwater planarians (Platyhelminthes, Tricladida) from the Iberian Peninsula and Greece: diversity and notes on ecology, Zootaxa 2779, pp. 1-38 : 30

Polycelis nigra (Müller, 1774)

( Figs. 3 , 18 A–C)

Material examined. ZMA V.Pl. 6880.1, River Miño in the "Ferri" de Goyan, Goyan, Pontevedra, Spain, 28 May 2005, sagittal sections on five slides; V.Pl. 6880.2, ibid., sagittal sections on two slides; V.Pl. 6881.1, River Miño in Ourense city, Spain, 0 3 March 2002, sagittal sections on three slides; V.Pl. 6881.2, ibid., sagittal sections on two slides; V.Pl. 6881.3, ibid., sagittal sections on two slides; V.Pl. 6882.1, River Uncín in the beach of Concha de Artedo, Lamuño, Asturias, Spain, sagittal sections on two slides; V.Pl. 6883.1, River La Muga, Les Escaules, Girona, Spain, sagittal sections on four slides.

Comparative discussion. Polycelis nigra is one of the most widespread freshwater planarians in Europe. However, it is extremely scarce in the Iberian Peninsula ( Fig. 3 ), where it had only been found in the basin of the river Muga, Girona Province ( Baguñà et al. 1980, 1981). We collected the species from five new Iberian localities: Galicia (three localities), Asturias (one locality, northwestern Spain) and Girona (one locality, northeastern Spain). Animals from Asturias reproduce sexually, as is usual in this species. The egg capsules are covered with a hemispherical envelope formed by a transparent, gelatinous or mucous substance ( Fig. 18 A).

After a period of starvation at 21 Cº in the laboratory, several specimens from the river Muga (that belongs to a previously known population) enveloped themselves in a transparent, oval-shaped capsule ( Fig. 18 B), apparently formed by secretions of their own mucus. The planarians were completely inactive inside the capsule. When forced to leave their envelope (18C), the worms returned to their normal active condition. The gelatinous envelope of the egg capsules as well as the envelope observed in encysted adult specimens suggest that Iberian populations of P. nigra have developed forms of resistance to desiccation or starvation.

Figures

FIGURE 3. Distributional records of twelve species of freshwater planarians in the Iberian Peninsula. Data from De Beauchamp, 1920; De Beauchamp, 1932; Baguñà et al. 1980, 81; Gourbault, 1981; Ribas, 1990; Sluys et al. 1995; Carranza & Giribet, 1997; unpublished records, this study.

FIGURE 18. Polycelis nigra, (A) egg capsule from a laboratory population originating from animals collected from the river Uncín near the beach of Concha de Artedo (Asturias, northern Spain), (B – C) specimen from the river Muga (Girona, northeastern Spain), (B) adult worm encysted, (C) adult worm at the moment of being forced to leave its envelope.