The genus Gobionellus and its six included species are diagnosed and redescribed. All species share a unique cephalic lateralis canal structure, which extends from the tip of the snout to above the rear margin of the operculum with an A‘BCDFHKL’ pore pattern; a vertical row of sensory papillae on the rear field of the operculum and transverse suborbital rows; and a blunt, distally flared fourth neural spine that is spatulate in five of the six species. Three species are found in the eastern Pacific Ocean. Gobionellus daguae is known only from the lower portions of rivers in Panama and Colombia. Gobionellus liolepis has been collected in tidepools and on beaches along the coast of Panama, in the Miraflores locks, and over mud habitats up to 20 m deep off El Salvador. The third eastern Pacific species, Gobionellus microdon, is widespread in estuaries and in some fresh waters from Mexico to Ecuador. Gobionellus mystax is a junior synonym of this species. Two species are recognized from the western Atlantic Ocean. Gobionellus oceanicus is found in estuaries and inshore coastal waters from New Jersey to southern Brazil. The other species, Gobionellus stomatus, is limited to Brazilian estuaries. Gobionellus occidentalis is the only member of the genus from western Africa, where it inhabits tropical estuaries and coastal waters. A key to the species is provided.