THE PHYLOGENETIC POSITION OF THE ASPIDOBOTHREA WITHIN THE PARASITIC FLATWORMS INFERRED FROM RIBOSOMAL-RNA SEQUENCE DATA

Sequence data from parts of the small subunit ribosomal RNA gene (18s rRNA) from an aspidobothrean and two digeneans have been added to a published data set which includes sequences from a number of parasitic and non-parasitic flatworms. Parsimony and distance matrix analyses of the data were carried out. Tests for particular clades were done using bootstrap resampling methods, and tests of particular topologies done using 4- and 5-taxon tests. The aspidobothrean Lobatostoma manteri emerges from near the base of the Neodermata, but whether as a sister group to the rest of the Neodermata or as a sister to the Digenea alone cannot be determined from the number of nucleotide sites available. Gyrocotyle is included with the cestodes in a very strongly supported clade in all analyses. There is evidence that the Monogenea is a paraphyletic group, although more data are needed to confirm this possibility.