A new species of Ergasilus (Copepoda: Cyclopoida: Ergasilidae) from coastal fishes of the Mexican Pacific

A new species of the cyclopoid copepod genus Ergasilus is described based on adult female specimens removed from the gills of the yellow snapper Lutjanus argentiventris and the yellowfin snook Centropomus robalito from a Pacific coastal system of Mexico. The new species Ergasilus davidi sp. n. has a combination of characters that includes a two-segmented first leg endopod, a three-segmented fourth leg endopod, and the presence of a single seta on the first antennular segment. These characters are shared with 14 other congeners known mainly from Brazil and North America. It differs from these other species in the armature and ornamentation of legs 1 and 4, the shape of the body, and the structure and ornamentation of the antennae. Additional characters include a maxillar basis armed with blunt teeth, distally bent maxillular setae, and naked margins of first exopodal segments of legs 2-4. The new species represents the first Ergasilus described from Mexican waters of the Pacific.