The study of 4 dasyatid stingrays—Dasyatis centroura (Mitchill, 1815), D. americana Hildebrand and Schroeder, 1928, D. say (Lesueur, 1817), and D. sabina (Lesueur, 1824)—from the northwestern Atlantic and the Gulf of Mexico showed the presence of monocotylid monogeneans Thaumatocotyle Scott, 1904 in their nasal fossae. Specimens collected from D. centroura from the northern Atlantic were identified as T. dasybatis (MacCallum, 1916). This confirmed the incorrect type host attribution of D. pastinaca (Linnaeus, 1758), which does not occur in the geographic area where T. dasybatis was described. Monogeneans collected from D. americana and D. say in the western Atlantic and the Gulf of Mexico were identified as T. longicirrus Hargis, 1955 and T. retorta Hargis, 1955, respectively, which corresponds to the opposite hosts attributed for each parasite species compared with their original description in the Gulf of Mexico. The species T. roumillati de Buron and Euzet, 2005 described from D. sabina in the northwestern Atlantic is reported for the first time in D. sabina from the Gulf of Mexico. Results clarify confusion in the literature regarding the hosts and habitats of Thaumatocotyle from dasyatids of the western Atlantic and Gulf of Mexico and support the oioxenous specificity of these monogeneans as well as their specificity for the nasal fossae of their hosts.