Crustaceans groom their olfactory organ, the antennules, by wiping them through a pair of mouthpart appendages. Antennular grooming behavior (AGB) can be stimulated in four different species of lobsters by at least one chemical (l-Glutamate (Glu)) found in food. However the one crab species tested thus far was unresponsive. In an effort to determine whether chemically-mediated AGB in the Reptantia is present only in the Macrura (lobster taxa) and lacking in the Meiura (crab taxa), we tested for AGB to chemical stimuli in seven reptantian species in the taxa Palinura (Palinurus elephas, Scyllarides aequinoctialis, S. nodifer), Astacidea (Enoplometopus debelius, Procambarus clarkii), Brachyura (Hemigrapsus sanguineus), and Anomura (Clibanarius tricolor), and one non-reptantian decapod in the taxon Caridea (Palaemonetes pugio). Because asymmetric setae on the lateral flagella of the antennules are the sole source of chemosensory input driving AGB, we also examined antennules for asymmetric setae using SEM. Significant AGB responses to chemical stimuli relative to control seawater was observed in all the macrurans tested with the exception of P. clarkii. E. debelius responded to glycine (Gly) and alanine (Ala), Scyllarides spp. to Gly, Ala, and aspartate, and P. elephas to Gly, Ala and methionine. In the meiurans, a weak but significant response to one chemical stimulus was observed in H. sanguineus, while no responses to chemical stimuli were observed in C. tricolor. Asymmetric setae were observed in all but one of the reptantian species (P. clarkii) but were aligned laterally along the tuft region of the macrurans and medially in the meiurans. The nonreptantian P. pugio did not show any AGB responses to chemical stimuli and lacked asymmetric setae. We propose that laterally-positioned asymmetric setae and chemically-mediated AGB are characters derived in the Macrura.