A new species of ascaridoid nematode, Hysterothylacium anguillae sp. n. (family Anisakidae), is described based on specimens recovered from the stomach and intestine of the giant mottled eel Anguilla marmorata Quoy et Gaimard from the Mngazi River, South Africa, collected in March–April 2011. It is characterized mainly by poorly developed lateral alae, a very short intestinal caecum and a long ventricular appendix, spicules 1.11–2.14 mm long (representing 5.2–5.8 % of body length), number of caudal papillae (19–21 pairs of preanals, 2 adanals and 5 postanals), presence of a median precloacal papilla (= ventromedian organ), tail tips of both sexes covered by minute spines, and by the shape and structure of lips. This is the first nominal species of Hysterothylacium described from an African freshwater fish and the second species of this genus reported from freshwater eels of the family Anguillidae. The following Indian congeneric species are considered species inquirendae: Hysterothalacium aetobathum Lakshmi, 2005, H. carutti Lakshmi, Rao et Shyamasundari, 1993, H. channai Lakshmi, 1995, H. fossillii Lakshmi, 1996, H. japonicum Rajialakshmi, 1996, H. kiranii Lakshmi, 1993, H. longicaecum Lakshmi, Rao et Shyamansundari, 1993, H. narayensis Lakshmi, 1997, H. nellorensis Lakshmi, 1996, H. neocornutum Rajialakshmi, Rao et Shyamasundari, 1992 and H. punctati Lakshmi, 1995. Of them, H. japonicum and H. neocornutum are transferred to Iheringascaris Pereira, 1935 as I. japonica (Rajialakshmi, 1996) comb. n. and I. neocornuta (Rajialakshmi, Rao et Shyamasundari, 1992) comb. n.