Integrative taxonomic study of mononchid nematodes from riparian habitats in Bulgaria. I. Genera Bastian, 1865 and Jairajpuri & Khan, 1977 with the description of sp. nov. and a key to the species of .

The species diversity of the genera Bastian, 1865 and Jairajpuri & Khan, 1977 was assessed in a study of the mononchid nematodes from a wide range of riparian habitats in Bulgaria. Four species were identified based on morphological and morphometric data: (de Man, 1880), Bastian, 1865, , and sp. The first three species were characterised both morphologically and molecularly (18S and 28S rRNA gene sequences) and the integration of these data and phylogenetic analyses provided support for their distinct species status. This paper provides detailed descriptions, morphometric data for multiple species populations, drawings and photomicrographs, and the first taxonomically verified sequences for ( = 6), (sensu stricto) ( = 4) and ( = 3). Comparative sequence and phylogenetic analyses suggested that the utility of the 18S rRNA gene for species delimitation is rather limited at least for some species complexes within the genus . At the generic and suprageneric level, the 18S and 28S rDNA phylogenies both recovered the three genera represented by two or more species (, , and ) as monophyletic with strong support, the Mononchidae as paraphyletic, the Anatonchidae as monophyletic, and there was no support for a sister-group relationship between and . A key to the species of is provided to facilitate the identification of the currently recognised 31 species.