Specimens of the ectoparasitic harpacticoid Balaenophilus manatorum (Ortíz, Lalana, and Torres, 1992) (Copepoda: Harpacticoida) were collected recently from the skin of sea turtles nesting along the Pacific coast of central Mexico. Adult specimens were compared with descriptions of specimens collected around Japan and Cuba. The intra-Pacific and the northwestern Atlantic specimens differed in subtle character states of the antennule, antennal exopod, swimming legs 1–4, and female and male fifth legs. Differences were within the range of intraspecific variability, as inferred from (1) the level of morphological divergence of B. manatorum from its only congener, Balaenophilus unisetus, also an epibiont of marine vertebrates, (2) the broad distribution of both species as a result of their widely ranging hosts, and (3) morphological differences, which were not geographically consistent. No differences were found between specimens collected from different host species, which are presumed to have different migration patterns and geographic ranges.