A new species of jawfish,Opistognathusthionyisp. n., is described from the Vitória-Trindade Chain and Fernando de Noronha Archipelago off Brazil, a disjunct distribution of ca. 1,800 km.Opistognathusthionyiand its allopatric Caribbean sister-species,Opistognathusmaxillosus, both have a wide, fan-like upper margin of the subopercular flap and mostly over-lapping meristic data. The new species differs fromO.maxillosusin having the darkest spot on the spinous dorsal fin, when present, between spines 2–5, versus always present between spines 6–9, the buccal area surrounding the esophageal opening pale versus very dark and fewer oblique scale rows in longitudinal series (45–52 vs. 69–85). A second new species,Opistognathusvicinussp. n., known from Brazil’s mainland, has completely over-lapping meristic values with its allopatric Caribbean sister-speciesO.whitehursti, but differs in lacking vomerine teeth and a supramaxilla and retaining the juvenile color pattern of the latter species in adults. Diagnoses, photographs, an identification key, and distributional maps are given for all Brazilian species ofOpistognathus.Molecular phylogenetic analysis of partial cytochrome c oxidase subunit-I sequences indicates that specimens of the two allopatric pairs,O.thionyi–O.maxillosusandO.vicinus–O.whitehursti, form reciprocally monophyletic groups that differ from each other on average by 9 to 11%, with less than 1% average pair-wise genetic distance within-species. Similar patterns of phylogenetic structure were observed between reciprocally monophyletic (predominately allopatric) groups within nominal species ofOpistognathusaurifrons, suggesting the possibility of at least two additional undescribed species from the Brazilian Province.
