Ceratocolax tavaresi n. sp. (Copepoda: Bomolochidae) parasitic in the Tomtate Grunt Haemulon aurolineatum Cuvier, 1830 (Actinopterygii: Haemulidae) off Rio de Janeiro, southeastern Brazil.

PURPOSE: A new species of the genus Ceratocolax Vervoort, 1965 is described based on specimens collected from the Tomtate grunt Haemulon aurolineatum Cuvier, caught in the coast of Angra dos Reis, off the State of Rio de Janeiro, Brazil.

METHODS: One hundred specimens of H. aurolineatum were purchased from the local fish market and examined for parasitic copepods. Parasites were fixed and preserved in 80% ethanol. Morphological features of the copepods were examined and drawn using an Olympus BX51 equipped with a drawing tube.

RESULTS: Ceratocolax tavaresi n. sp. can be distinguished from all congeners by the following combination of characters in the adult female: (1) second endopodal segment of leg 3 with one seta, (2) lack of stout spinules along outer margins on rami of legs 2-4, (3) genital somite without flaplike structures, (4) terminal exopodal segment of leg 4 with seven elements; and in the adult male: (1) legs 1 to 4 with 3-segmented rami (except endopod of leg 4), (2) presence of a pair of blunt processes on dorsal surface of the third pedigerous somite, (3) second endopodal segment of leg 3 with one seta.

CONCLUSION: The number of species of Ceratocolax reported in the Atlantic Ocean was increased to three, including the new species. This is the forty-second species of copepod found parasitizing haemulid fish in marine waters from the Americas; however, the diversity of parasitic copepods off this continent is still underestimated.