Bopyrid isopods are obligate ectoparasites of other crustaceans, occurring on copepods as larvae and on decapods as adults. They are characterized by a marked sexual dimorphism in the adult stages and are associated with a number of metabolic and structural alterations in definitive hosts. Pachycheles monilifer (Dana, 1852) is a porcellanid crab broadly distributed in the western Atlantic whose parasitic fauna has never been studied. 136 crabs were collected from Cipara Beach, Sucre State, Venezuela. The crabs were preserved in 70% ethanol, sexed, measured and reviewed for the presence of bopyrids. The measurements of the crabs were 4.28 ± 1.51 mm (CL) and 4.51 ± 1.79 mm (CW). The parasite obtained was identified as Aporobopyrus bonairensis MarkhamM, 1988. Infestation was typically unilateral, with slightly more being found in the left branchial chamber. General prevalence was 20.59%, although the majority of occurrences were noted from female hosts. The parasite caused deformation of the branchial cavity in 89.3% of the hosts. Bopyrids were present in all size classes of porcellanids, having a positive correlation of prevalence with CW. Intensity of infestation was 1.55 ± 0.60, being slightly greater in males. Female parasites measured 3.08 ± 0.77 mm (TL) and 2.01 ± 0.44 mm (MW). The parasite distribution in relation to host sizes evidenced an early association between bopyrids and crabs. Likewise, high prevalence of parasites in the larger size classes could indicated a low energetic impact of Aporobopyrus bonairensis on Pachycheles monilifer. This is the first report of this bopyrid on a host outside the genus Petrolisthes, the first record of A. bonairensis in Venezuela, and the first record of any parasites for Pachycheles monilifer.