The present paper deals with the Anasca and Ascophora Imperfecta of the inland bays of Curaçao and Bonaire. Collections were made by P. WAGENAAR HUMMELINCK (1930, 1936/ 37, 1948/49, 1955, 1963/64, 1968, 1970, and 1973) and by the author (1982), and stored in the collections of the Rijksmuseum van Natuurlijke Historie, Leiden. A total of 25 species – almost all occurring in inland bays – are described here and fully illustrated. Six new species are established: Crassimarginatella harmeri. Scrupocellaria curacaoensis, Scrupocellaria carmabi, Scrupocellaria piscaderaensis, Scrupocellaria hildae and Bugula hummelincki. Attention is given to the ecology of the species. The bays have been compared as to species composition in relation to substrate and conditions during collecting.