Xenophyophores, a group of agglutinated rhizopod protists, occur in nearly all the world's oceans at depths generally in excess of 1OOO m. In certain areas they dominate deep-sea, megafaunal communities. Their widespread distribution indicates a well-established adaptive radiation. Only one fossil analogue, however, has been proposed. This is Paleodictyon, a trace fossil that superficially resembles the Recent infaunal xenophyophore Occultammina profunda in morphology. The platy xenophyophore genus Psammina closely resembles certain late Palaeozoic fossils from northeastern Kansas that have been referred to as ‘phylloid algae’. Here we compare modern xenophyophore structure with that of the fossil phylloids. By reconstructing the fossils, analysing their thin sections with polarized, blue, and ultraviolet light and subjecting them to Q-switched laser ablation, we conclude that certain phylloids could represent shallow-water xenophyophores. ***Phylloid algae, xenophyophores, motphology, reconstruction, laser ablation, Pennsylvanian.