| Summary: | The strongyloid nematode subfamily Phascolostrongylinae comprises parasites of the large intestine and stomach of Australian macropods and wombats. In this study, we tested the phylogenetic relationships among the genera of the Phascolostrongylinae using the first and second internal transcribed spacers of the nuclear ribosomal DNA. Monophyly was encountered in the tribe Phascolostrongylinea comprising two genera, <i>Phascolostrongylus</i> and <i>Oesophagostomoides,</i> found exclusively in the large intestine of wombats. The tribe Hypodontinea, represented by the genera <i>Hypodontus</i> and <i>Macropicola</i> from the ileum and large intestine of macropods, was also found to be monophyletic. The tribe Macropostrongyloidinea, comprising the genera <i>Macropostrongyloides</i> and <i>Paramacropostrongylus,</i> was paraphyletic with the species occurring in the stomach grouping separately from those found in the large intestines of their hosts. However, <i>Macropostrongyloides</i><i>dissimilis </i>from the stomach of the swamp wallaby and <i>Paramacropostrongylus toraliformis</i> from the large intestine of the eastern grey kangaroo were distinct from their respective congeners. This study provided strong support for the generic composition of the tribe Phascolostrongylinea. The unexpected finding of <i>M. dissimilis</i> and <i>P. toraliformis</i> being distantly related to their respective congeners suggests a requirement for future taxonomic revision that may warrant separation of these species at the generic level.
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