Margollus bokanicus n. sp., collected from natural habitats in Khorasaneh district, Bokan,West Azarbaijan province, Iran, is described. Morphological and morphometric data are provided as well as drawings and light microscopy illustrations. The new species is characterized by a medium size body length (0.60 to 0.73 mm), labial and postlabial sclerotizations, lip region 7-mm wide, offset by constriction and long neck (167 to 207 mm), long pharyngeal basal bulb (27 to 36 mm) or 16% to 17% of total neck length, female genital system monodelphic–opisthodelphic, anterior branch reduced to a uterine sac (26–29 mm) or 1.1 to 1.3 times the body diameter, long posterior uterus (25–28 mm) or 1.1 to 1.3 times the body diameter, V = 40 to 47, cylindroid female tail (17 to 24 mm, c = 31 to 38, c’ = 1.1 to 1.4), and males unknown. This taxon is easily distinguishable from other Margollus species by its smaller general size and more posterior vulva. A compendium of Margollus species is also presented.
