A population of the rarely collected aulolaimoidid genus, Oostenbrinkia, was recovered from the rhizosphere soil of Fagus orientalis in Mazandaran province, north Iran. Oostenbrinkia pedrami n. sp. is mainly characterized by long females, 920 µm with a 6 to 8 µm long odontostyle, 18 to 21 µm long odontophore with well-developed basal flanges, 124 to 187 µm long neck, vulva post equatorial (V = 58.5-61.0), and tail short (10-18 µm long, c = 42.5-65.2, c′ = 0.6-0.9) and rounded. Compared to the generotype species, O. oostenbrinki, the new species has a longer odontostyle, total stylet, a posteriorly located vulva, and shorter rounded tail, and compared to the only one other representative, O. parva, longer females with longer odontostyle and total stylet. In molecular phylogenetic analyses using a near-full-length sequence of the small subunit ribosomal DNA (SSU rDNA), the new species appeared as an independent basal lineage to the included ingroup species. This is the first molecular data of this family.
