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.