Sets of small ribosomal DNA (SSU rDNA) and large ribosomal DNA (LSU rDNA) sequences were obtained for Philometroides moraveci Vismanis Yunchis, 1994, Philometra kotlani (Molnár, 1969), Philometra rischta Skrjabin, 1923, Philometra cf. obturans (Prenant, 1886) (Philometridae), Sinoichthyonema amuri (Garkavi, 1972), Agrachanus scardinii (Molnár, 1966), Kalmanmolnaria intestinalis (Dogiel Bychowsky, 1934) and Skrjabillanus tincae Shigin Shigina, 1958 (Skrjabillanidae). Phylogenetic analysis of SSU rDNA data shows that dracunculoid nematodes are divided into two well-supported clades designated as Clade I and Clade II, respectively. Clade I includes the type species of the genus Philonema Kuitunen-Ekbaum, 1933, some species from the family Daniconematidae Moravec Køie, 1987 and two subfamilies of skrjabillanids, Skrjabillaninae Shigin Shigina, 1958 and Esocineminae Moravec, 2006. Clade II unites species from the families Dracunculidae Stiles, 1907, Micropleuridae Baylis Daubney, 1926 and Philometridae Baylis Daubney, 1926. Within the Philometridae, there are several well-supported groups of species, one of which unites freshwater Philometra spp. from the Palearctic cyprinids, identified as P. kotlani, P rischta, P. ovata (Zeder, 1803) and P. cyprinirutili (Creplin, 1825). However, the phylogenetic relationships of most philometrids are unresolved. An analysis of partial SSU and LSU rDNA sequences indicates that there is no direct phylogenetic relationship between Agrachanus Tikhomirova, 1971 (type species Skrjabillanus scardinii Molnár, 1966) and Skrjabillanus Shigin Shigina, 1958 (type species Sk. tincae), which means that the genus Agrachanus can be resurrected. Our study confirms that Philonematinae Ivashkin, Sobolev Khromova, 1971 should be elevated to the family rank. We formally establish the family Philonematidae Ivashkin, Sobolev Khromova, 1971 stat. nov. We also suggest combining the superfamilies Dracunculoidea Stiles, 1907 and Camallanoidea Railliet Henry, 1915 into the infraorder Camallanomorpha Roberts, Janovy Nadler, 2013.
Keywords: Nematoda, Agrachanus, Chromadorea, Camallanomorpha, Dracunculoidea, nematodes, Philometridae, Philonematidae, phylogeny, Skrjabillanidae, SSU rDNA.