| - Sinopse:
The karyotypes of four species of freshwater triclads of the genus Girardia, i.e. G. schubarti, G. tigrina, G. anderlani, and G. biapertura, from populations of different localities of the Rio Grande do sul State, in southern Brazil, were analyzed. The karyotype of G. biapertura is presented for the first time. Three basic compleents of 4, 8, and 9 chromosomes were found. Diploids, triploids, or mixoploids (2n/3n) specimens were frequently detected in these populations. The basic chromosomal complement of n=9 was verified in two different species, presenting a large acrocentric chromosome which is rare in the family dugesiidae. An intra and interspecific chromosomal variability was also detected and its evolutionary implications are discussed.