‘A monograph on the Polychaeta of Southern Africa’ by J. H. Day, published in 1967 and covering over 700 species, was considered an essential reference text for marine biologists. Nonetheless, despite the major contribution it has made, we now know that the biodiversity of Polychaeta (commonly known as bristleworms) in southern Africa has been underestimated by more than 500 species. As one of the top 20 polychaete families highlighted as requiring revision in southern Africa, direct observation of magelonids in the collections of Iziko Museums of South Africa and Natural History Museum, London identified by John Day, and additional material has been carried out. This has revealed that the original description of Magelona capensis was based on two species. Consequently, an additional redescription of the holotype of M. capensis is provided herein, and the additional material is described as Magelona ekapa sp. nov. The new species shares similarities with eight species comprising the ‘Magelona pitelkai group’,