Bitentaculate Cirratulidae (Annelida, Polychaeta) collected chiefly during cruises of the R/V Anton Bruun, USNS Eltanin, USCG Glacier, R/V Hero, RVIB Nathaniel B. Palmer, and R/V Polarstern from the Southern Ocean, Antarctica, and off Western South America.

Forty-one species in five genera of bitentaculate cirratulids are reported from new collections from South America, the Southern Ocean, and seas around Antarctica. Twenty-seven species are new to science; one new genus is described to deal with some species formerly identified as Chaetozone. New records, synonymies, and new combinations are reported. Previous records are reviewed with type specimens of most species reexamined and redescribed. The sub-Antarctic species Aphelochaeta cincinnata (Ehlers, 1908) does not occur in Antarctica: the numerous published records of this species instead belong to several new species. The types of Tharyx epitocus Monro, 1930, and Tharyx fusiformis Monro, 1939, have spines in posterior setigers and are referred to other genera. Among the 41 species treated in this study, 11 belong to Aphelochaeta, eight are new; eight species belong to Caulleriella, six are new; six species belong to Chaetocirratulus n. gen., three are new; 12 species belong to Chaetozone, seven are new; and four species belong to Tharyx, three are new. Numerous samples come from slope and abyssal depths, expanding our knowledge of the distribution of Southern hemisphere deep-sea cirratulids.