Mouthparts of four cooccurring haustoriid amphipods (Neohaustorius schmitzi, Protohaustorius aff. deichmannae, Acanthohaustorius millsi, and Pseudohaustorius caroliniensis) were examined with the scanning electron microscope to determine if structural differences exist between the species. Mandibular palp setation differs in arrangement, size, number, and shape of cup-like comb setae on segment 3. The plates of the maxilliped also differ in the four species. These morphological differences could be an important isolating factor enabling the species to fractionate the food resources within a restricted area.