ABSTRACT
Three new species of monogeneans parasitic on the gills and esophagus of Trichiurus lepturus (Linnaeus, 1758) in the Southern Brazilian coast are described herein. Between July 2006 and June 2007, 120 specimens of T. lepturus were acquired from local fishermen in Guanabara Bay (23152S, 43º1156W), Rio de Janeiro State, Brazil. Pseudempleurosoma guanabarensis sp. nov. (Dactylogyridae) presented 15% prevalence and mean intensity 1.8, and differs from all congeners by presenting larger body, largest rectangular dorsal bar, and larger MCO with muscular sheath in the base. Encotyllabe souzalimae sp. nov. (Capsalidae) showed 7.5% prevalence and mean intensity 1.3, differs from all congeners by the size and position of the testes, morphology of the MCO, and morphology and size of the anchors. Octoplectanocotyla travassosi sp. nov. (Plectanocotylidae) showed 8.3% prevalence and mean intensity 1.5, and differs from all congeners by presenting a third pair of smaller hooks between the outer (more robust) and inner pair (thinner and larger); number and shape of the genital spines and shape of the clamp sclerites.