A new species of Tortanus (Atortus) Ohtsuka, 1992 (Copepoda, Calanoida, Tortanidae) from Great Nicobar Island, north-eastern Indian Ocean

A new planktonic copepod assigned to the subgenus Tortanus (Atortus) Ohtsuka, 1992 is described from Great Nicobar Island, Andaman and Nicobar archipelago. The new species Tortanus (Atortus) dhritiae sp. nov. belongs to the tropicus-group. The new species can be distinguished from all other species of the tropicus-group by the presence of a notch on the left lateral joining of fourth and fifth pedigerous somites, asymmetrical caudal rami with a rounded process originating from the anterior portion of the left ramus produced over to the right, and an elliptical shaped exopodal lobe of leg 5 with distolateral curved seta in female. In male, serrated ridge on the anterior one-third surface of segment XX of the right antennule, obtuse trapezoid-shaped right leg 5 coxa with triangle-shaped medial process, semi-circular basis with slight curve near base and crocodilian head-shaped medial process with small process distally and bearing one distal and one medial setae.