The taxonomic status of Skrjabinalius guevarai Gallego & Selva, 1979 (Nematoda: Pseudaliidae) and the synonymy of Skrjabinalius Delyamure, 1942 and Halocercus Baylis & Daubney, 1925.

Within the cetacean lungworm family Pseudaliidae Raillet & Henry, 1909, the distinction between the two genera of the subfamily Halocercinae Delamure, 1952, i.e. Halocercus Baylis & Daubney, 1925 and Skrjabinalius Delyamure, 1942, is principally based on the structure and shape of the male copulatory bursa. In species of Halocercus, the bursa is unlobed, whereas in the two species included in Skrjabinalius, S. cryptocephalus Delyamure, 1942 and Skrjabinalius guevarai Gallego & Selva, 1979, the bursa is described as clearly lobed. During a parasitological analysis of cetaceans from the Spanish Mediterranean, we collected a number of specimens of S. guevarai with variable levels of bursal lobulation, including individuals with unlobed bursae. Examination of voucher specimens of the type-species of Halocercus, H. delphini Baylis & Daubney, 1925, collected from cetaceans in the North-East Atlantic revealed the same variations in bursal shape, and the same arrangement of bursal rays and papillae. A morphometric comparison did not reveal substantial differences between both species. Moreover, Maximum Likelihood and Bayesian Inference analyses of the second internal transcribed spacer (ITS2) sequences of 11 specimens of S. guevarai and one of H. delphini grouped both species together, regardless of bursal shape, in a highly supported clade within the Pseudaliidae. Accordingly, we consider S. guevarai as a junior synonym of H. delphini. The great variability found in bursal lobulation in the type-species of Halocercus invalidates the use of this trait as a genus-level diagnostic character and, therefore, Skrjabinalius should also be considered synonymous with Halocercus.