A new species of Sciadicleithrum [Monogenea, Dactylogyridae] parasitic on Geophagus brasiliensis [Perciformes, Cichlidae] from Guandu River, Southeastern Brazil

Sciadicleithrum guanduensis sp. nov. is described from the gills of the cichlid fish Geophagus brasiliensis (Quoy et Gaimard, 1824) from Guandu River, Seropédica, Rio de Janeiro, Brazil. The new species differs from all congeners by the accessory piece of the male copulatory organ, which comprises a small, delicate sheath with articulated appearance, and by the presence of a large unique umbelliform membrane on the ventral bar.