Schmidtea polychroa (Schmidt, 1861)

Schmidtea polychroa is distributed mainly in the northern part of the island in large hydrographic basins as well as small rivers (Fig. 2). On the basis of karyological and reproductive characteristics four biotypes (A, B, C, D) have been recognized within the species (Benazzi, 1957; Benazzi & Benazzi Lentati, 1976).

The first record of S. polychroa from Sardinia by Benazzi (1957) reported the presence of biotype A, which is amphimictic and diploid (2n = 8; n = 4). Pala and co-workers (Pala et al., 1980b; Casu et al., 1982; Vacca et al., 1988, 1993) highlighted the widespread distribution of biotype A and found also several populations characterized by triploid (3n = 12; n = 4) and tetraploid chromosome sets (4n = 16; n = 4), corresponding to the gynogenetic, asynaptic biotypes C and D, respectively. Biotype B was never found in Sardinia. Further, a new pentaploid biotype (5n = 20; n = 4) was found in a population from River Temo for which the type of development is unknown (Casu et al., 1982) (Fig. 2).