His most controversial contributions were in his work on the Ediacaran assemblages, which he and Friedrich Pflüger (1994) suggested, based on their constructional morphology, to be pneu structures unrelated to modern metazoans. While this view has been steadily opposed by many workers, it gained some ground as the affinities of many of these organisms have remained resistant to analysis. Seilacher considered many of these taxa to be giant xenophyophores, i.e. large rhizopodal protists. He appeared in the film Volcanoes of the Deep Sea, going on a dive on the DSV Alvin to investigate modern analogues of the trace fossil Paleodictyon.