Larvae of the grapsid crab Armases angustipes DANA, 1852 (originating from the coast of the state of São Paulo, Brazil) were reared in the laboratory from hatching to the megalopa stage. In this paper, the morphology of the four zoeal stages and the megalopa is described and illustrated. Morphological comparisons are made with all descriptions that have become available for the larvae of this genus (including an unpublished description of A. angustipes; Kowalzuck, 1994) and of some closely related genera (Aratus, Sesarma). Several differences to the previous description of A. angustipes are shown, and additional characters such as the previously undescribed cephalotoracic setation of the larval stages are described and illustrated. Diagnostic characters are provided to differentiate the American genera Sesarma and Armases.