The studies on freshwater Triclads from Corsica were initiated by ARNDT , who showed, among other things, the wide distribution of a planarian ascribed by him to Planaria gonocephala Dugès [=Dugesia gonocephala (Dugès)]. Afterwards, Benazzi demonstrated that this planarian belongs in reality to a different species, which later on was named Dugesia benazzii by Lepori; this species is present also in Sardinia and Capraia. During two excursions (1949-1965) planned by our Institute, many samples of this planarian were collected from different localities of Corsica; interesting peculiarities, concerning the chromosome complement and the reproductive modalities, were found in the different populations. A third excursion, made in 1968 by Dr. Mazza and me, allowed us to get further information on this subject. Most of the samples belong to the amphimictic diploid biotype, with 2n=16, n=8 (specimens from Suerte, Patrimonio A and B, Golo, Navaccia, Belgodere A, Favone, Cavo, light-coloured specimens from Oso, Canalli). In some specimens, especially those which reproduce mainly by fission (populations from Conca and Bravone), hyperdiploid sets were observed; the sexual specimens possess oocytes with a various number of univalents, bivalents and trivalents. In fact, these fissiparous populations periodically produce sexual specimens, which, however, frequently come again to fission. In dark-coloured specimens from Oso completely asynaptic oocytes were found. In Rizzanese and Bicchisano populations, oocytes of two types (hexaploid and triploid) are present, as well as in Loreto and Roccapina populations already studied in our Institute. A statistical analysis demonstrated that, in the Rizzanese samples, the hexaploid oocytes are more frequent (88,37%) and the individual variations very slight. The Rizzanese population looks like the one from Loreto; they both could have the same genetica! condition. I have tried to illustrate the geographical distribution of the different populations in relation to the chromosome complement. As to the populations with two types of oocytes, their distribution in a rather small area seems to confirm the hypotesis of their hybrid origin helped by their isolation. No apparent relationship between the reproductive modalities (sexual or fissiparous) and the geographical distribution has been found.
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