Investigations of the marine pelagic tunicate genus Thalia Blumenbach, 1798, resulted in the description of two new species, T. cicar and T. sibogae. In addition the three known subspecies of Thalia democratica (Forskål, 1775) are considered full species. The distribution of these species, including Thalia longicauda (Quoy & Gaimard, 1824), is given and a key to the solitary and aggregate zooids of the species is added. The specific status of the six taxa of the genus is discussed.