Grooming behaviour in South American freshwater aeglid crabs (Aegla platensis and A. uruguayana) involves primarily the third maxillipeds and fifth pereiopods. The third maxilliped grooms the eyes, antennules and occasionally the antennae with fields of sword and serrate setae. The crista dentata located on the ischium of the third maxilliped cleans the dactyli of the second, third and fourth pereiopods. The fifth pereiopod is chelate but opens only slightly. This appendage grooms the gills, carapace, abdomen and pleopods with the denticulate margins of the chela and specialized composite setae of the propodus and dactylus. Grooming behaviour and general morphology of grooming appendages in aeglids resemble those of their marine relatives in the Anomura rather than those of other freshwater decapods. This observation supports Bauer's (1981) contention that grooming may serve as an indicator of phyletic affinity.