Karyology and karyotype analysis of diploid freshwater planarian populations of the Dugesia gonocephala group (Platyhelminthes, Tricladida) found in Sardinia

Karyology and karyotype analysis were carried out on freshwater planarian p opulations of the Dugesia gonocephala group. The strains studied were all d iploid with chromosomic number 2n = 16; n = 8. They came from 12 sites main ly localized on the west of the island of Sardinia. Three karyotypes indica ted with the letters A, B and C were found in which eight homomorphic pairs of chromosomes were easily identified. In karyotype A all chromosomes are metacentric. Ten populations of the twelve examined showed this karyotype w hich appears to be the most common. In karyotype B the seventh pair of chro mosomes is submetacentric. This karyotype is quite common having been previ ously found in another eight Sardinian localities. Karyotype C differs from the others in having submetacentric third and seventh pairs of the chromos ome complement. It was found in only one locality. The differences observed between these three karyotypes could be interpreted either as sign of diff erentiation at species level, or as an intraspecific variation due to chrom osome mutations (pericentric inversions).