Popolamento planariologico dei fiumi del nord Sardegna: 1. I cariotipi delle planarie d'acqua dolce del gruppoDugesia gonocephala(Tubellaria, Tricladida) presenti nel fiume Silis (Sassari)

Karyological investigations were carried out on tail regenerative blastemata of 104 (95 sexual and 9 fissiparous) out of 270 freshwater planarians belonging to theDugesia gonocephalagroup collected at five different sites along the Silis river (North Sardinia). The results revealed that the SilisDugesia gonocephalas.l. is made up of different karyotypes: (1) diploid karyotype with 14 chromosomes identified asDugesia hepta; (2) diploid karyotype with 16 chromosomes and (3) triploid karyotype with 24 chromosomes, both attributable respectively to the amphimittic diploid and gynogenetic triplo-exaploid biotypes ofDugesia benazziiLepori; (4) karyotype with 22 chromosomes; (5) karyotype with 32 chromosomes and (6) karyotype with 27 + B chromosomes of fissiparous individuals. The basic haploid set from which the last three types could have derived could not be determined since, although the chromosome number of sets was essentially constant, the composition varied considerably not only between individuals but al so within the same individual.