Redescription of Caligus serratus Shiino, 1965 (Copepoda: Caligidae) parasitic on eleven fish species from Chamela Bay in the Mexican Pacific.

Caligus serratus Shiino, 1965 (Copepoda: Caligidae), a parasite on 11 fish species caught in Chamela Bay off the Pacific Coast of Mexico, is redescribed based on material found on Pacific agujon needlefish Tylosurus pacificus (Steindachner, 1876). Caligus serratus can be distinguished from its congeners by the combination of the following characters: i) short abdomen (approximately 0.2 times as long as cephalothorax), ii) pointed posteromedial process on the first segment of the antenna, iii) sternal furca with bluntly pointed, diverging tines, and iv) leg 4 exopod bearing 3 unequal, distal spines (the shortest 0.2 times the length of the longest). Microphotographs of female and illustrations of both female and male are provided. The redescription of this species might be useful given its low host specificity.