Gymnophionan amphibians are characterized mainly by having elongated bodies and lack of limbs and are poorly known because of their secretive life habits. Most species are fossorial, although some are aquatic or semiaquatic. We describe a new species of semiaquatic caecilian, genus Chthonerpeton, from a transition area between the Caatinga and Cerrado biomes, along the coastal vegetation of the State of Piauí, northeastern Brazil. The new species is very similar to Chthonerpeton perissodus and Chthonerpeton noctinectes in annular counts but differs in number of cloacal denticles, color pattern, position of tentacle aperture, and number of teeth.