Dugesia hepta Pala, Casu & Vacca, 1981

Dugesia hepta is a Sardinian endemic species restricted only to four hydrographic basins in the northwestern part of the island (Pala et al., 1981; Stocchino et al., 2005) (Fig. 1). The species is characterized by a peculiar chromosome number (2n = 14; n = 7), from which derives its specific epithet, which is unique within the Palaearctic Region. This chromosomal pattern is known only for Dugesia ryukyuensis Kawakatsu, Oki, Tamura & Sugino, 1976, and D. batuensis Ball, 1970, both from eastern Asia (Ball, 1970; Kawakatsu et al., 1976). Dugesia hepta is also morphologically well distinguishable because of a peculiar dorsal ejaculatory duct with a lateral opening and a ventro-lateral penial fold. Among Dugesia species this dorsal course of the ejaculatory duct character is shared by only one other species viz. D. superioris Stocchino & Sluys, 2013 from Lake Ohrid in Albania (Stocchino et al., 2013b, 2017c). Dugesia hepta populations are exclusively sexual with a life cycle comparable to that of other European dugesiids, such as D. ilvana Lepori, 1948 from Elba Island and D. gonocephala (Dugès, 1830) from Central Europe (cf. Stocchino & Manconi, 2013). A recent origin of D. hepta from D. benazzii was suggested by molecular analysis (Lazaro et al., 2009). This hypothesis is also supported by the coexistence of the two species at many localities in all of the Sardinian hydrographic basins inhabited by D. hepta.