A review of collections of triplefin blennies of the genus Enneanectes from the tropical western Atlantic Ocean reveals a new species, Enneanectes flavus n. sp., belonging to the unscaled-abdomen subgroup. The species is distinguished by having mature adults with black spinous dorsal fins and mature males with a bright yellow rear body and tail; other distinctive features include the third and fourth body bars closer together than the fourth and fifth, the last dark body bar usually extending onto the basal third of the caudal fin, three dark blotches along the anal fin, and two black blotches on each side of the anterior body. The species is apparently limited to the southeastern corner of the Caribbean Sea, i.e. northeast Venezuela and Tobago (and photographs from St. Vincent), where it replaces the widespread Redtail Triplefin, Enneanectes matador. This species is added to the small set of endemic marine species in this corner of the tropical western Atlantic Ocean, likely adapted to unusual local oceanographic conditions. The mtDNA-barcode COI sequence of the new species is 2.4% divergent from the two related allopatric lineages of E. matador in the Caribbean. A revised key to the 9 species of Enneanectes in the Greater Caribbean is presented.