Additional morphological data and first genetic characterization on females of Micropleura vazi Travassos, 1933, parasitic in Caiman yacare from Brazil, with comments on the phylogeny of Dracunculoidea (Nematoda)

Species of Micropleura Linstow, 1906 (Dracunculoidea: Nematoda) are common parasites of crocodilians worldwide. Studies related to this genus remain scarce, particularly regarding genetic characterizations, due to the difficulty in obtaining the parasite specimens. Although the morphology of M. vazi Travassos, 1933, a parasite of Caiman spp. in the Neotropics, has been previously evaluated, some morphological inconsistencies persist, and certain features are insufficiently described. Moreover, there is no genetic data for the species. In this regard, we provide the first genetic characterization of M. vazi along with detailed morphological analysis using light and scanning electron microscopy (SEM). We report for the first time in M. vazi the presence of phasmids and of oesophageal gland nuclei, in addition to provide a clearer view of the cephalic region and the accurate position of the vulva. Genetic characterization of the species was conducted using partial sequences of the 18S and 28S rDNA, and the phylogenetic reconstructions using these first indicated the monophyly of Micropleura and of most families within Dracunculoidea. Moreover, Micropleuridae appears to be the sister group to Dracunculidae, and Philonematidae should be considered valid as it is not close to Philometridae. Furthermore, Anguillicolidae should be allocated in another superfamily, Anguillicoloidea, which is basal relative to Dracunculoidea and far from it. The absence of males in the current sampling may suggest a seasonal occurrence of these parasites, as has been reported for other dracunculoid nematodes.