Neoechinorhynchus (Neoechinorhynchus) dorsovaginatus n. sp. (Acanthocephala: Neoechinorhynchidae) is described from the dusky kob, Argyrosomus japonicus (Temminck & Schlegel) from the southern coast of South Africa in the Breede River Estuary. Like four other species of Neoechinorhynchus Stiles & Hassall, 1905, N. (N.) africanus Troncy, 1969, N. (N.) johnii Yamaguti, 1939, N. topseyi Podder, 1937 and N. (N.) tylosuri Yamaguti, 1939, the new species has a very long, slender body, cylindrical testes and cement-gland, anterior proboscis hooks much longer than the middle or posterior hooks, and a long neck. The new species is the only species of Neoechinorynchus having an antero-dorsal hump just posterior to the neck and a specialised vaginal sphincter and a gonopore on the dorsal side. It is closest to N. (N.) johnii, but is distinguished from it by: the size of the trunk, proboscis, anterior proboscis hooks, neck, and the posterior testis in relation to the cement-gland; the shape of cerebral ganglion and proboscis hook root; and the number of giant nuclei in the cement-gland.