A new species of Hourstonius is described from the northern coast of São Paulo State. Hourstonius wakabarae sp. nov. is distinguished from the other species of the genus by the morphology and the size of the accessory flagellum of antenna 1, the articles of antennae 1 and 2, the mandibular molar, and the telson. The new species H. wakabarae lives associated with macroalgae growing on rocky shores, especially the brown alga Sargassum, at depths up to 2-3 m. This is the first species of the genus Hourstonius recorded from Brazilian waters.
Amphipoda; Amphilochidae; Hourstonius; Macroalgae; Taxonomy