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1 February 2007 Biogeography and Karyotypes of Freshwater Planarians (Platyhelminthes, Tricladida, Paludicola) in Southern Brazil
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In the Tricladida (Platyhelminthes), the incidence of different biotypes identified by several ploidy levels is very common. Planarians collected in the State of Rio Grande do Sul were identified using cytogenetics. Different species distributions were observed with respect to Rio Grande do Sul's geomorphology, which could have been caused by their different microhabitats. Girardia tigrina and G. anderlani consisted of diploid and triploid individuals, whereas G. schubarti showed diploids, triploids, and mixoploids; for all these species, individuals of different ploidies were sympatric. Only for diploid G. anderlani were B chromosomes observed. These B chromosomes seem to have an irregular segregational behavior during mitosis, and possibly also during meiosis. However the processes (e.g., selection, mutation) of maintaining 2n, 3n, and 2n/3n individuals within natural populations of G. schubarti remain to be clarified.

Tanise Knakievicz, Adriana Helena Lau, Daniel Prá, and Bernardo Erdtmann "Biogeography and Karyotypes of Freshwater Planarians (Platyhelminthes, Tricladida, Paludicola) in Southern Brazil," Zoological Science 24(2), 123-129, (1 February 2007).
Received: 24 January 2006; Accepted: 1 September 2006; Published: 1 February 2007

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