At present, it is commonly accepted that the taxa Nassarius costulatus (Brocchi, 1814), N. ferussaci (Payraudeau, 1826), N. cuvierii (Payraudeau, 1826), N. unifasciatus (Kiener, 1835), and others belong to a single species, very common and variable. However, we have concluded that a species complex exist, because at least two different species of this complex are present in the coasts of SE Spain, N. cuvierii and N. unifasciatus. The protoconch, teleoconch, head-foot characters, radula, egg capsules and type of larval development have been studied. The main differences between both species are the size of the shell, the protoconch and, specially, the egg capsules. A neotype of N. cuvierii has been designated.