All attached epifaunal species have the potential to colonize floating substrates such as driftwood, externally shelled cephalopods, Sargassum-like algae and marine vertebrates. Such pseudoplankton are preserved in a much wider range of facies than their benthic relatives. However, they are never as abundant as benthos due to the rarity of attachment sites. Pseudoplanktonic species utilize five attachment strategies: cemented, adpressed, pendent, boring and clinging. Overcrowding appears to be a common problem on floats and consequently the pendent strategy, with its limited attachment area relative to the size of the organism, appears to have been favoured by obligate pseudoplankton. However many species are facultatively pseudoplanktonic, making palaeoecological interpretations difficult. Most reported examples of pseudo-plankton, particularly those from black shale facies, are too abundant to be attributed to this group and, in the majority of cases, a benthic mode of life is more plausible. The fossil record of pseudoplankton is thought to be considerably poorer than has hitherto been suggested. Evaluation of the literature reveals a low, although variable diversity of pseudoplanktonic populations through the Phanerozoic. High diversity in the mid-Palaeozoic is due to the presence of large orthoconic nautiloids which provided ideal floating substrates for a number of groups. Unexplained diversity minima occurred in the Permian and Cretaceous.