We describe herein a new species of the abundant polychaete family Syllidae, Exogone brasiliensis sp. nov. The new species is characterized by a peculiar morphology of anterior body falcigers, with shafts and blades modified specially in chaetigers 1 and 2; falcigers until chaetiger 5 different from those of the rest of the body; and dorsal simple chaetae from midbody onwards unique in the genus, nearly straight, subdistally swollen in one side only, distally rounded. Exogone brasiliensis sp. nov. is described based on detailed morphological analyses under optical and scanning electron microscopes, and compared to its most similar congeners.