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A collection of ascidians from 100–1000 m deep off the north-western coast of Australia has yielded 19 species, including one new, two possibly endemic to the north-western coast of Australia, four well-known Indo-west Pacific tropical species and 12 species known from the deeper waters of the western Pacific, of which 11 had not previously been recorded from off the western Australian coast or from other parts of the Indian Ocean. A third of these 12 species displays adaptations for a reduction in filter-feeding capacity, as do other known species from deeper slope and abyssal habitats. Nevertheless a connection with fauna of deep ocean basins of the Indian Ocean is not apparent at this stage. The full range of characters associated with species, genera and families are discussed, and those contributing to the identification of immature or mutilated specimens, as well as those relevant to an assessment of phylogenetic relationships, are emphasized.

During the Spanish expedition CIEMAR 99/00, on board the BIO‐Hesperides, 30 species of ascidians (distributed in 13 genera and eight families) were collected using a rock dredge in the Bransfield and Gerlache straits. Most of them were already known, but one species, Tetrazona ciemari sp. nov., is new for science. Additional morphological data are provided for six species. Five are reported for only the second time and the known distributions of five species are extended.

Fifty-one species are discussed of which five are new. Of the remaining 46 species, 20 previously known from one to three records and 11 more frequently recorded have their known geographic range and/or range of morphological variation extended and the synonymy of a further 15 species is revised. Taxonomic problems, including phylogeny, are addressed in Rhopalaea crassa, Pycnoclavella detorta, Ecteinascidia spp. and Plurella (see Phallusia polytrema). New species are Sigillina pulvinus, Polyclinum corbis, Perophora longicaulis, Stolonica brevigastra and Botrylloides saccus.

Thirty-four species of benthic Tunicata are recorded in the deep-water material collected from 255 to 8116m 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 7694–7934m 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.

Four aplousobranch ascidians (Aplidium conicum, Polycitor adriaticus, Cystodytes dellechiajei, Eudistoma mucosum) from the northern Adriatic Sea are redescribed. Gonads and larvae of three of them are observed for the first time.