On the identity of Eucephalobus oxyuroides (de Man, 1876) Steiner, 1936 (Rhabditida, Cephalobidae), with an updated taxonomy of the genus and notes about its phylogeny

The identity of Eucephalobus oxyuroides is discussed after studying two Iberian populations that fit the original description of the species. A new characterization is consequently provided as follows: 0.49 to 0.70 mm long body, lip region continuous with the adjoining body and bearing short probolae prongs, neck 132 to 158 µm long, spermatheca 23 to 47 µm long or 1.0 to 1.8 times the corresponding body diameter, post-vulval uterine sac 40 to 54 µm long or 2.0 to 2.5 times as long as the body diameter, V  =  58 to 64, female tail conical elongate with very acute terminus (60-79 µm, c = 7.1-10.0, c′ = 4.9-5.8), male tail conical (36-49 µm, c =10.9-14.3, c′ = 2.4-3.4) with an elongate acute mucro, and spicules 21 to 22 µm long. Previous records of the species are revised. An emended diagnosis of the genus is proposed, and its taxonomy is updated with a list of species, key to their identification and illustrations. The evolutionary relationships of Eucephalobus, as derived from the analyses of 18S and 28S rDNA fragments, reveals that it occupies a basal position within the subfamily Cephalobidae.