A karyological study on populations of Dugesia gonocephala s.I. (Turbellaria, Tricladida)

A karyological analysis was carried out on sexual and fissi-parous populations of planarians belonging to the ’Dugesia gonocephala group’, collected in localities of the Mediterranean area, Morocco, and Yemen. Euploid (diploid and triploid) chromosome sets are observed in populations reproducing only sexually, whereas hyperdiploid and aneutriploid complements characterize agamous and fissiparous strains. Aneuploidy may occur either associated with an increase in the chromosome number or as a product of rearrangements in numerically balanced chromosome sets. Mitotically unstable B-chromosomes are present in all aneu-ploid populations. The variety of karyological characteristics encountered is discussed from a cytogenetic and cytotaxonomic standpoint.