The euglenoids are largely freshwater, flagellated protists belonging to the excavate branch of the eukaryotic supertree. Euglenoid cells are covered by a pellicle composed of distinctive, interlocking longitudinal strips of protein-rich heteropolymers. A few workers have noted a similarity between the encysted forms of extant euglenoids and the fossil palynomorph Pseudoschizaea. Similar discoidal palynomorphs marked with concentric striae may represent a Phanerozoic series of euglenoid fossil cysts. The Ordovician-Silurian microfossil, Moyeria cabottii, was previously interpreted as euglenoid based on morphological criteria. We extracted M. cabottii from the Fish Bed Formation (Silurian of Scotland). Its wall ultrastructure shows distinctive frames consisting of Ï€-shaped XX plateaus and shallow U-shaped heels, which are fused to form the pellicle wall. This structure is consistent with the extant euglenoid pellicle. Moyeria cabottii and Moyeria sp. occur in lacustrine shales of the 1.078 Â± 24 Ga XX Nonesuch Formation (USA). This extends back considerably the first occurrence of euglenoids and is consistent with molecular phylogenetic studies that posit their basal position near the root of the eukaryotic supertree. Moyeria now joins a handful of Precambrian fossils with well-established ties to crown groups in the eukaryotic supertree, and provides a useful minimum constraint calibration for molecular clock analyses.