Acanthogyrus (Acanthosentis) barmeshoori n. sp. (Quadrigyridae) is described from the Persian tooth-carp, Aphanius farsicus Teimori, Esmaeili, and Reichenbacher, 2011 (Cyprinodontidae) in the Maharlu Lake basin, southern Iran. Aphanius farsicus is an endemic freshwater fish found in streams and springs that drain into Maharlu Lake, Shiraz, Iran. The new species is the smallest of all the 44 known species of the subgenus Acanthosentis Verma and Datta, 1929, measuring between 0.26 and 1.68 mm in length. It is further distinguished by having a short cylindrical proboscis with very long anterior hooks widely separated from very small hooks in 2 very close circles posteriorly (hook length ratio about 4:1). It is separated from 4 other species of Acanthosentis with similar proboscis armature but with less-extreme diversification of hook length. The new species is also distinguished in having anterior para-receptacle structures (PRS) and a similar posterior structure like those reported in only 1 other species of Acanthosentis from Japan. Proboscis receptacle is single walled with a large triangular cephalic ganglion. Testes are large, pre-equatorial, and Saefftigen's pouch is prominent. Fourteen to 25 circles of spines cover the anterior 50–70% of the trunk, but a few spines may be present at posterior end of trunk. This is the first species of Acanthosentis where SEM images, showing external morphological details, are provided. From a total of 357 fish specimens examined between July 2006 and June 2007, 173 specimens (48.5%) were infected with individuals of the new species. The prevalence of infection decreased with increasing fish size. The parasite was observed all year, with the highest abundance and intensity in May while the prevalence was highest in February. The prevalence of acanthocephalans decreased with increasing fish size. While most worms were recovered in fish within the length range of 18–29.9 mm, 1 of the longest parasites (1.68 mm long) was found in fish within the range of 30–33.9 mm long.