Filenchus aquilonius is redescribed based on population found from rizosphere of Ziziphus zizyphus in Southern Khorasan province, Iran. F. aquilonius is characterized by: Lip region rounded, not offset, with fine annuls; four incisures in lateral line; Stylet moderately developed, 10-11.8 µm long with rounded knobs; Excretory pore between nerve ring and basal esophageal bulb; Hemizonid immediately in front of excretory pore; Deirids at the level of excretory pore; Vagina perpendicular; Spermatheca an axial chamber and offset pouch; Tail about 120-157 µm, tapering gradually to a pointed terminus. The large subunit expansion segments of D2/D3 were performed for, F. aquilonius to examine the phylogenetic relationships with other Tylenchids. DNA sequence data revealed that F. aquilonius had closet phylogenetic affinity with Irantylenchus as a sister group with high BI (100%) and with other Filenchus species for this region and placed them in one clade with high BI percentage (100%). 28S gene strongly supports that Filenchus species are monophyletic. Phylogenetic position and additional information of other taxa in Tylenchidae from this region of Iran are included.

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