Affinities of the Gyliauchenidae: utility of the 18S rRNA gene for phylogenetic inference in the Digenea (Platyhelminthes).

18S rRNA sequences were analysed using parsimony and distance matrix methods to infer relationships among 8 species of trematodes. In particular, the disputed relationships of the digenean family Gyliauchenidae were examined. This family is regarded by some to be close to the Lepocreadiidae, and by others to be close to the Paramphistomidae. The data gave very strong support for placing the Gyliauchenidae close to the Lepocreadiidae, and almost no support for the alternative hypothesis. This support was found, regardless of the method of analysis, using data from different regions of the molecule as well as from the entire molecule. Morphological features are re-interpreted in the light of this conclusion.