A new genus and a new species of Eulimidae are described based on the shell morphology and on the host-parasite relationship of the type species. Eulimacrostoma microsculpturata Souza & Pimenta gen. nov. and sp. nov. parasitizes a starfish of the genus Luidia and has an elongated, conical, straight, or slightly curved shell, a protoconch with a brownish spiral band and convex whorls, a peculiar large and broad aperture with a strongly protruding outer lip, and microsculpture of axial lines on the teleoconch. Four other species are included in the genus, all from the western Atlantic: Eulimacrostoma chascanon (Watson, 1883), comb. nov., Eulimacrostoma fusus (Dall, 1889), comb. nov., Eulimacrostoma lutescens (Simone, 2002), comb. nov., and Eulimacrostoma patula (Dall & Simpson, 1901), comb. nov. Newly available material of Eulimacrostoma patula expands the known geographic distribution of this species in the Caribbean to the north coast of Brazil. Eulimacrostoma chascanon and Eulimacrostoma fusus and Eulimacrostoma lutescens are known only by the type series which was re-examined. A redescription is provided for Eulimacrostoma chascanon and Eulimacrostoma fusus. Species within Eulimacrostoma differ mainly by teleoconch sculpture, the presence or absence of an umbilical fissure, and shell dimensions. Lectotypes are designated for Eulimacrostoma chascanon, Eulimacrostoma fusus, and Eulimacrostoma patula.