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 pu blished data set which includes sequences from a number of parasitic a nd 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 em erges from near the base of the Neodermata, but whether as a sister gr oup to the rest of the Neodermata or as a sister to the Digenea alone cannot be determined from the number of nucleotide sites available. Gy rocotyle is included with the cestodes in a very strongly supported cl ade in all analyses. There is evidence that the Monogenea is a paraphy letic group, although more data are needed to confirm this possibility .