The diagnosis of Diplectanocotyla (Monogenoidea: Dactylogyridea) is emended, the genus is transferred to the Diplectanidae, and the Diplectanocotylidae is considered a junior synonym of the Diplectanidae. Diplectanocotyla megalopis is redescribed from gills of Atlantic tarpon, Megalops atlanticus (Megalopidae), from the Atlantic coasts of Nicaragua and Mexico (new host and locality records). Although D. megalopis was previously found on the Atlantic tarpon in Puerto Rico, the species from this host was originally misidentified as Diplectanocotyla gracilis. Diplectanocotyla is differentiated from other diplectanid genera by its members having a haptor with 2 central suckers (1 ventral, 1 dorsal) and paired ventral bars, a pair of squamodiscs with concentric rows of scales, a spined tegument of the posterior trunk and peduncle, an ovary looping the right intestinal cecum, and a vas deferens looping the left intestinal cecum.