Description of <italic>Deladenus hebetocaudatus</italic> n. sp. (Rhabditida: Neotylenchidae) from northern Iran.

<italic>Deladenus hebetocaudatus</italic> n. sp. was recovered from rotten wood samples of a dead broad-leaved forest tree, collected from forests of the city of Savadkooh, northern Iran. It was described and illustrated using morphological and partial SSU rDNA data. Females of the new species were mainly characterised by their 540-625 <italic>μ</italic>m long body and conical tail with a wide blunt mucron-like differentiation at tip. They were further characterised by eight lines in lateral fields, 8.5-9.5 <italic>μ</italic>m long stylet, pharyngo-intestinal junction at level with nerve ring, vulva at 89.7-91.0% of body, the vulva to anus distance 2.4-2.8 times vulval body width, presence of 9.2-11.0 <italic>μ</italic>m long postvulval uterine sac (PUS), sperm inside female reproductive system and no males recovered. The new species was morphologically compared with free-living phase females of all known species under the genera <italic>Deladenus</italic>, <italic>Hexatylus</italic> and <italic>Rubzovinema</italic>. The morphological differences of the new species with four species of <italic>Deladenus sensu lato</italic>, namely <italic>D. ipini</italic>, <italic>D. megacondylus</italic>, <italic>D. saccatus</italic> and <italic>D. ulani</italic>, having a PUS in their free-living phase, were discussed. The phylogenetic relationships of the partial SSU rDNA sequence of the new species with other relevant sequences of related taxa were reconstructed using Bayesian approach and the resulting topology was discussed. [ABSTRACT FROM AUTHOR]