The first articulated specimen of Plumulites canadensis (†) from the Upper Ordovician of Ontario, with a review of the anterior region of Plumulitidae (Annelida: Machaeridia)

Articulated plumulitid machaeridians are rarely preserved intact. Here, we describe a complete specimen of Plumulites canadensis (Woodward, 1889) retaining much of the head region. The two anteriormost pairs of shell plates are quite distinct from the rest in outline, density of concentric rugae, and especially the radial ornamentation of the second pair. We demonstrate that the latter condition is present in other complete plumulitids and therefore widespread, which elucidates a larger diversity in morphology of plumulitids than realized previously