A molecular cytogenetic comparison of planarians from the 'Dugesia gonocephala group' (Platyhelminthes, Tricladida)

Planarians belonging to the Dugesia gonocephala group share extensive karyo type similarities when compared using classical cytological techniques. How ever, after in situ hybridization with rDNA, differences in localization an d number of rDNA loci were identifiable among the species. Species-specific features in the rDNA structure have been observed by restriction pattern a nalysis. A family of long interspersed repealed elements (De1), isolated in Dugesia etrusca, and conserved only in some species of the group, was also informative in establishing specific genomic relationships among the speci es. We suggest that an understanding of the organization and evolution of r epeated DNA sequences can be a useful tool for studying molecular mechanism s of evolutionary significance in planarians.