Pseudorhabdosynochus riouxi is a species of diplectanid monogenean parasitic on the gills of dusky grouper Mycteroperca marginata.

It was described by Guy Oliver in 1986 as Cycloplectanum riouxi,[2] then transferred to the genus Pseudorhabdosynochus by Santos, Buchmann & Gibson in 2000.

[3] Pseudorhabdosynochus riouxi is a small monogenean, 0.3 mm in length.

The name of the species, riouxi, honours Professor Jean-Antoine Rioux, "as President of the Société Française de Parasitologie".

[2] The type-host is the dusky grouper Mycteroperca marginata (Perciformes, Epinephelidae) sometimes designated by its synonyms in parasitological publications (Epinephelus guaza or Epinephelus marginatus).