A cladistic analysis of the tribe Labiostrongylinea Beveridge, 1983 (Nematoda: Cloacinidae) parasitic in macropodoid marsupials (Marsupialia: Macropodoidea), with a redescription of Parazoniolaimus collaris Johnston & Mawson, 1939.

Morphological characters of both adult and juvenile representatives of the genera comprising the Labiostrongylinea (Strongylida: Cloacinidae: Cloacininae) were examined to prepare an amended description of Paralabiostrongylus bicollaris, a redescription of Parazoniolaimus collaris and a cladistic analysis of the tribe. A cluster of Wallabinema spp., with a fleshy collar on which amphids and deirids are borne, was used as the outgroup for the analysis. The 50% consensus tree, bootstrapped through 1000 replicates, derived from the cladistic analysis had a basal polytomy of Dorcopsinema and Paralabiostrongylus; and a crown polytomy of Labiosimplex, Labiomultiplex, Parazoniolaimus, Labiostrongylus and Potorostrongylus. This analysis provided reasonable evidence for considering all 7 clades as being of generic status and amended diagnoses were prepared. The morphology of the cephalic end of fourth stage juveniles, cephalic papillae and amphids lying posterior to the lips, gave support to the contentions that a fleshy collar is a plesiomorphic character and that Dorcopsinema is the most primitive genus within the group. There was, however, insufficient support from morphological data to provide a robust resolution of generic relationships. Host and biogeographical data were indicative of Paralabiostrongylus and Labiosimplex having been derived from ancestral Dorcopsinema, then Labiostrongylus, Labiomultiplex and Parazoniolaimus derived from ancestral Labiosimplex, and Potorostrongylus from ancestral Labiomultiplex. Additional data, derived from molecular sequencing, is needed to help resolve the relationships within the tribe.