MOLECULAR PHYLOGENETICS OF TURBELLARIA DEDUCED FROM THE 18S RIBOSOMAL-RNA SEQUENCING DATA

PCR and sequencing methods were employed to study the 18S rRNA gene 5' -terminal nucleotide sequences of Turbellaria species from the Baikal Lake. Twenty species from five individual turbellaria orders were stud ied [Tricladida (10), Lecithoepitheliata (5), Prolecithophora (3), Pro seriata (I), and Kalyptorhynchia (1 species)]. For each order represen ted by more than one species, consensus sequences were determined and were further used in phylogenetic analysis by the maximum parsimony an d distance matrix methods. The bootstrap technique was employed to eva luate the statistical validity of relatedness revealed by phylogenetic analysis. Analysis of rooted trees constructed by the Fitch-Margolias h method allowed identification of a monophyletic group including Kaly ptorhynchia, Proseriata, and Lecithoepitheliata with a bootstrap value of 100%. The molecular data contradict the traditional classification , according to which Tricladida and Proseriata are members of one and the same class Seriata, and the comparative anatomy data, which assert the relatedness of lower Prolecithophora and Lecithoepitheliata + Pro rhynchidae.