Sciadicleithrum juruparii n. sp. is described from the gills of the Neotropical cichlid fish Satanoperca jurupari (Heckel) caught in the Guamá River, in the delta of the Amazon River, at Belém, Pará State, Brazil. Diagnostic characters of the new species are a basally articulated male copulatory organ with clockwise coils and an accessory piece; a ventral bar with a median process; similar hooklets; vagina in the form of a sclerotised tube; and a sinistral vaginal aperture with a sclerotised papilla lying in a small surface depression. It is the only species of Sciadicleithrum Kritsky, Thatcher & Boeger, 1989 with a medial projection on the ventral bar.