A reconsideration of the diagnostic characters of Atya Leach and Atyoida Randall supports their generic separation. Accordingly, Atyoida is reinstated as a full genus of which the distinguishing features are slender third peraeopods with a relatively short merus, a tapering endopod in the male first pleopod and protandry. It includes three species, A. bisulcata Randall from the Hawaiian Islands, A. pilipes (Newport) widespread in the Indo-Pacific area, and A. striolata (McCulloch & McNeill) found only in Australia. A. striolata is fully redescribed. Morphological variation throughout its range is slight; no subspecies are distinguishable. It is suggested that larvae hatch in estuaries and that protandry is an adaptive life-cycle strategy.