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

Abstract

Karyological investigations were carried out on tail regenerative blastemata of 104 (95 sexual and 9 fissiparous) out of 270 freshwater planarians belonging to the Dugesia gonocephala group collected at five different sites along the Silis river (North Sardinia). The results revealed that the Silis Dugesia gonocephala s.l. is made up of different karyotypes: (1) diploid karyotype with 14 chromosomes identified as Dugesia 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 of Dugesia benazzii Lepori; (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