Deep-water ascidians from the south-western Atlantic (RV Dmitry Mendeleev, cruise 43 and Academic Kurchatov, cruise 11)

Thirty-four species of benthic Tunicata are recorded in the deep-water material collected from 255 to 8116 m from the south-western Atlantic, Scotia and Weddell seas. Maximum species diversity occurs at between 4000 and 6000 m. Unlike the north Atlantic, large forms predominate. However, that there are only a few species less than 5 mm is probably the result of the collecting method. Some species appear to form crowded populations of numerous specimens, as evidenced in the records of approximately 400 specimens of Agnezia at 7694-7934 m and 150 large specimens of Dimeatus at 5680-6145 m. Six new species are described, of which one is recorded from more than 8000 m. This is one of the greatest depths yet recorded for ascidians, the only other species recorded below 8000 m is Situla pelliculosa Vinogradova, 1969.