SSU RDNA CHARACTERIZATION OF LYMNAEID SNAILS TRANSMITTING HUMAN FASCIOLIASIS IN SOUTH AND CENTRAL-AMERICA

The small subunit (18S) rRNA gene sequences of the lymnaeid morphs I a nd II (Mollusca: Gastropoda: Basommatophora: Lymnaeidae) transmitting human fascioliasis in the high endemic zone of the northern Bolivian A ltiplano and of Lymnaea cubensis from Mexico and Guadeloupe island (Ca ribbean) have been obtained by direct polymerase chain reaction PCR cy cle sequencing and silver staining methods and compared to that of the 6 most common European Lymnaeidae species. Results allow us to establ ish definitively the distinction between the lymnaeids from the northe rn Bolivian Altiplano and L. cubensis. Lymnaea cubensis is a valid spe cies distributed in North and Central America but absent in the northe rn Bolivian Altiplano. Lymnaeid morphs I and II from the northern Boli vian Altiplano both present the same 18S rDNA sequence, which is moreo ver identical to that of the European species Lymnaea truncatula. Sign ificant nucleotide substitutions in helix E10-1 of the variable region V2 of the secondary structure suggest the need for distinguishing L. cubensis in the subgenus Lymnaea (Bakerilymnaea) with L. (B.) cubensis as type species. The subgenus Lymnaea (Fossaria) is retained, with L. (F.) truncatula as type species. The larger number of nucleotides in the ISS rDNA sequence of L. cubensis (1,860 bp) with regard to the oth er Lymnaea species (1,843-1,852 bp) is tentatively related to the more ancient paleogeographic origin of L. cubensis. The grouping of L. cub ensis with L. truncatula and the relationship of Lymnaea auricularia w ith Lymnaea peregra in the phylogenetic trees obtained show an evoluti onary parallelism with the digenean parasite species they transmit, na mely Fasciola hepatica and Fasciola gigantica, respectively.