A new species of the genus Doto is described from the Cape Peninsula of the Western Cape Province, South Africa. To date, the genus Doto is probably one of the more complex and poorly defined genera within nudibranchs. The very small body size and very similar external and internal features make this genus problematic and, therefore, poorly studied. Despite the large number of described species around the world, only three species are known to be present in South Africa: Doto coronata (Gmelin, 1791), Doto pinnatifida (Montagu, 1804) and Doto rosea Trinchese, 1881. Morphologically, Doto splendida sp. nov. is easily distinguished from all its South African congeneric species by its conspicuous colouration. In addition, mitochondrial and nuclear genes clearly separate the new species from other species from southern Africa. A molecular phylogeny based on two mitochondrial (COI and 16S) and one nuclear (H3) gene is herein presented. This phylogeny includes all available species of Doto (valid and unidentified...