Centropages orsinii Giesbrecht, 1889 (Copepoda, Calanoida, Centropagidae) from an anchialine cave in Vanuatu

The adult male of Centropages orsinii Giesbrecht, 1889 is redescribed based on a single specimen collected in an anchialine cave on the island of Espiritu Santo in Vanuatu. The mouthparts of this species have never previously been described and figured. Males exhibit a remarkable asymmetry in the form of the basis of leg 4. On the right leg only the basis carries three processes on its posterior surface, a unique asymmetry for the entire Calanoida. Comparison with males from other locations in the Indo-Pacific reveals some variation in the precise form of these processes. Some other species of Centropages exhibit sexually dimorphic asymmetry, with modified setation elements present on the exopod of right leg 4 only in males. It is speculated that this might be correlated with the strong asymmetry exhibited in females of some species within the genus.