A new species of ragworm belonging to the genus Perinereis is described from South Baja California Peninsula, Mexico. It was discovered in rocky intertidal zone among calcareous algae. The new species is characterized by the presence of a single-shield shaped bar paragnath on area VI and a remarkable development of dorsal cirrophore towards the posterior end. The new species is very close to P. ponteni described from Brazil, but they differ in the shape of the bar in area VI and in the relative size between the dorsal cirrus and the anterior part of the dorsal ligule in median parapodia.
