Abstract Storm-dominated siliciclastic shelf deposits in the upper half of the Upper Tiouririne Formation (Upper Ordovician, upper Berounian– c. Katian 1–2) of southern Morocco contain large specimens of at least two species of Archaeoconularia ( A . aff. consobrina and A . cf. imperialis ). Pseudoconularia cf. grandissima occurs in basal beds of the formation, but is far less abundant than Archaeoconularia . The large size of the Archaeoconularia (>500 mm long in some cases) suggests gigantism induced by cold, nutrient-rich waters. Specimens preserving the apical end terminate in a schott, indicating that the conulariids were severed near the apex prior to final burial. Many of the Archaeoconularia occur in monospecific aggregations in which the component specimens exhibit preferential alignment, probably owing to entrainment and burial by storm currents or flows. Some Archaeoconularia are encrusted by edrioasteroids and/or craniid brachiopods, which in certain cases are so closely spaced as to interfere with growth. The edrioasteroids and brachiopods were probably epibionts attached to living, erect or semi-erect conulariids that were partially infaunal. More generally, Late Ordovician conulariid assemblages of South Polar Gondwana and adjacent terranes exhibit low generic diversity relative to those of low- to mid-latitude terranes (Baltica and Laurentia), and are dominated numerically by Archaeoconularia .