Some 1700 plankton net hauls (642 on the slope reglon of the continental shelf and 1100 in neritic waters) were made during surveys carried out by F.R.V. Wavreen (C.S.1 R., Division of Fisheries) in the eastern Australian Pacific Ocean area between latitudes 24�S. and 44�S from 1938 to 1941. The Tunicata. Euphausiacea, Hyperiidae. Chaetognatha, and Pteropoda totalling 118 species in the slope and shelf hauls were identified by various authors. In this paper 27 species which were frequently a part of each other's biological environment in the slope plankton, were assorted into groups: (1) by the use of an index derived from the corrected geometric mean of the joint occurrence of pairs of species, following Fager and McGowan (1963); and (2) by assessing the significance (using X 2 ) of the departure of a joint occurrence from an expected value calculated on the basis of empirical probability for each pair of species. Groups were set up according to the method of Fager (1957). The tests yielded similar results. Groups found, using test (2), and their tentative water mass affiliations were follows. (i) Central Tasman and south-west Tasman: GROUP A, Sagitta planctonis, S. lyra, S. minima, Krohnitta subtilis, Eukrohnia hamata; GROUP B, Thysanoessa gregaria, Euphausia recurva, N. dificilis, E. spinifera. (ii) South equatorial and Coral Sea: GROUP C, Oikopleura fusiformis, O. cophocerca, O. longicauda; GROUP D Stegosoma magnum, Megalocercus huxleyi, Oikopleura rufescens, Traustedtia multitentaculata, Doliolum denticulatum; GROUP E, Sagitta hexaptera, Pterosagitta draco, S. regularis, S. serratodentata pacifica, S. bipunctata, S. enflata, S. ferox, S. robusta, and Stylocheiuon carinatum. Recent references to the grouped species are discussed. The major affiliations and the temperature, chlorinity, and latitudinal ranges of the three forms of Sagitta serratodentata (tasmanica, atlantica, and pacifica) are set out and a tentative list of the water mass preferences of a number of the ungrouped species is given.