Three known species of the family Criconematidae namely Criconema crotaloides, C. princeps and Ogma zernovi were recovered from natural forests in Golestan province, and were characterized based upon their morphological and morphometric characters. The Iranian population of C. crotaloides was recovered from the rhizosphere of Fraxinus excelsior and is characterized by females 517-594 μm long, having 64-70 not retrorse body annuli with smooth margin without lateral differentiation and RV = 11-14. The second species, C. princeps, was associated with Carpinus betulus and is characterized by females 421-506 μm long, having 63-69 rounded to retrorse body annuli with smooth margin, marked by distinct lateral triangular arches and RV = 11-12. The main characteristics of this species and the status of some other previously reported populations as C. princeps were discussed. The last species, Ogma zernovi, was recovered from the rhizosphere of Quercus sp., and is characterized by females 350-653 μm long, having 58-64 retrorse body annuli, each annulus with nine rows of short smooth scales in the middle of the body, the scales uni- or bi-lobulated, RV = 9-11, tail conoid and the last three annuli without projections. New observations on its morphology were added, comparisons were made with the type populations of the species and characteristics of the species were updated with including data of males and juveniles. Compared to the type populations, no remarkable differences were observed for the three studied species. All the three species represent new records for Iran.