Intra- and interspecific variation in the intersetular distance (i.s.d.) of some southern Australian cladocerans was examined. The seasonal range of i.s.d. inDaphnia carinata adults (2.34±0.07 mm) was 0.17–0.25 µm. I.s.d. increased with increasing body size forD. carinata andD. thomsoni. Variation in i.s.d. between nine adult cladoceran taxa (several of which coexisted) also was examined; significant differences did occur, but the size range was small (0.14 to 0.58 µm). The possibility that intersetular distances are an index of niche separation based upon the capture of different particle sizes is discussed.