Abstract Neoechinorhynchus brentnickoli n. sp. is described from specimens of Dormitator latifrons (Pacific fat sleeper) collected from 3 localities along the Pacific Coast of Mexico: Tres Palos Lagoon (Guerrero State), Bahia de Chamela (Jalisco State), and Mazatlan (Sinaloa State), Mexico. Of the 3 members of the genus known from Mexican fish, the new species is more similar to Neoechinorhynchus golvani Salgado-Maldonado, 1978, than to Neoechinorhynchus roseus Salgado-Maldonado, 1978, or Neoechinorhynchus chimalapasensis Salgado-Maldonado, Caspeta-Mandujano, and Martinez-Ramirez, 2010. Neoechinorhynchus brentnickoli n. sp. can be distinguished from N. golvani in being longer and having more dimorphism between trunk length of males and females, a different number of ventral giant nuclei (2 vs. 1), smaller proboscis, shorter hooks in all 3 circles, a longer receptacle, and larger testes and cement gland. The anterior portion of the trunk wall of the new species is more delicate than that of the rest of the...