Members of Polymorphidae, including Hexaglandula corynosoma, are acanthocephalans commonly found as intestinal parasites in marine mammals, fish-eating birds and waterfowl. Hexaglandula corynosoma is distributed throughout the Southeastern U. S. and southwards to Puerto Rico and Brazil. An acanthocephalan (and its larvae) resembling H. corynosoma were found parasitizing intermediate (decapod crustaceans, Uca spinicarpa) and definitive hosts (yellow-crowned night herons, Nyctanacea violacea) from various localities in Mexico. A morphological and genetic study, in combination with previous studies, confirmed that the larvae and adults were conspecific and corresponded to H. corynosoma. This is the first record of H. corynosoma in Mexico parasitizing intermediate and definitive hosts.