Ever since Q-mode factor analysis has been applied to microfossil data, investigators have attempted to determine whether statistical groupings of species in deep-sea sediments are ecologically meaningful. We address this question for radiolaria using living, death, and sediment assemblages from the equatorial Pacific. Of the seven sediment assemblages identified from a basin-wide analysis, four are important in the tropics. Eastern boundary and transitional sediment assemblages identify ecological environments similar to living assemblages. The western Pacific sediment assemblage does not appear to represent a natural grouping of species. The dominant, tropical sediment end-member represents a combination of warm water species from subtropical and western Pacific environments. Of the two the predominant signal in tropical sediments is that of the western Pacific. The implication of a sediment bias toward warm water species may be due to the lack of an important cold water indicator species, Lophophaena hispida, in the sediment analysis. ¿ 1998 American Geophysical Union