Gloiotrichus (Liagoraceae; Nemaliales), a red algal genus originally described from Western Australia and later found in Hawaii, is reported for the first time in the western Atlantic Ocean, from the Caribbean Sea. A new species, G. vermiculatus, is described based on specimens collected fromsubtidal waters near Carrie Bow Cay, Belize and off St. John, U.S. Virgin Islands. Features of the new species are compared with G. fractalis Huisman et Kraft (1994), the generitype, and only other species presently in the genus. Gloiotrichus vermiculatus differs reproductively; in having fewer cells in its carpogonial branch, (3-) 4 (-5) cells versus 5–8 cells for G. fractalis; and dioecious gametophytes while those of G. fractalis are monoecious. The timing of sterile lateral filament initiation from carpogonial branch cells varies between the two species, with G. fractalis generally initiating them before the first transverse division of the zygote, while those of G. vermiculatus are typically initiated concurrently or after the first division. The basal cell or other proximal cells of the sterile lateral filaments occasionally issue rhizoid-like filaments that can develop to a higher degree in G. vermiculatus, where they may loosely drape or encircle carpogonial branch cells. The new species differs vegetatively from G. fractalis in its longer (290–500 mm) and more complex primary cortical fascicles, which are trichotomously to polychotomously branched, not only at the basal division but at several inner divisions, thereafter the cortical filaments are subdichotomously branched outward, while those of G. fractalis are described as subdichotomously branched throughout.