A new species of trichosomoidid nematodes, Huffmanela mexicana n. sp., is established on the basis of its egg morphology and biological characters. The dark-shelled, embryonated eggs of this histozoic parasite occur in masses in the inner layer of the swimbladder wall of the bullseye puffer fish Sphoeroides annulatus Jenyns, 1843 (Tetraodontidae, Tetraodontiformes) off the Pacific coast of Mexico (Sinaloa State) and are characterized mainly by their shape and size (63–69 × 30–33 µm), an aspinose surface, relatively small polar plugs, and their thick egg wall (4–5 µm). A key to Huffmanela species based on egg morphology is presented.