The Drumian Wheeler Konservat-Lagerst€ atte of the House Range of Utah (Wheeler-HR) has yielded one of the most diverse exceptionally preserved Cambrian biotas of North America. The discovery of soft-bodied fossils invariably provides precious insights into this biota, given that most of its non-biomineralizing components are known from very few specimens. This contribution describes some 30 new exceptionally preserved fossils of Wheeler panarthropods. Two new species are recognized, the radiodont Hurdia sp. nov. A and the megacheiran Kanoshoia rectifrons gen. et sp. nov. Along with a species of Leanchoilia, K. rectifrons represents the first confident megacheiran record in these strata. The presence of the radiodont genus Amplectobelua and the isoxyid species Isoxys longissimus is reported outside of the Burgess Shale in Laurentia. New specimens of Caryosyntrips serratus, Naraoia compacta, Messorocaris magna and Mollisonia symmetrica provide insights into the phylogenetic affinities, local spatial distribution and morphological variation of these species hitherto known by single specimens in the Wheeler-HR. The same is true of new materials of the more common Pahvantia hastata and Perspicaris? dilatus. Formal descriptions of the order Mollisoniida ord. nov. and family Mollisoniidae fam. nov. are also provided. Last, the preservation of body structures other than the dorsal exoskeletons is illustrated for the first time in two common components of the fauna: the agnostid Itagnostus interstrictus and the bivalved euarthropod Pseudoarctolepis sharpi. The new material substantially improves our understanding of the diversity of the Wheeler-HR biota, and provides new evidence of its distinctiveness relative to the Wheeler biota of the Drum Mountains.

The recent re-interpretation of the Lower Palaeozoic euarthropod group Mollisonia as belonging to Chelicerata has triggered a renewed interest for the poorly known family Mollisoniidae. In this contribution, we revise the anatomy, taxonomic diversity, and systematics of Thelxiope, the sister-taxon of Mollisonia. This mollisoniid genus comprises four species, and is characterized by the presence of one cephalic, seven thoracic (one per tergite), and three pygidial long sagittal spines. The type species, T. palaeothalassia Simonetta & Delle Cave, is a rare taxon in the Wuliuan Burgess Shale Formation of Canada, which can be recognized by the hypertrophy of a single of its sagittal spines, the posteriomost one. T. spinosa (Conway Morris & Robison)–a species originally assigned to a distinct genus ‘Ecnomocaris’ herein synonymised with Thelxiope–is known from a single specimen found in the Drumian Wheeler Formation of the House Range of Utah. It differs from the type-species in the hypertrophy of both the anteriormost (cephalic) and the posteriormost (third pygidial) sagittal spines. The same Wheeler strata have also yielded a single specimen of a new taxon, T. holmani sp. nov., which lacks hypertrophied sagittal spines and features blunt thoracic tergopleural tips. A putative fourth species, referred to Thelxiope sp. nov. A, extends the stratigraphical range of Thelxiope to the Lower Ordovician (Tremadocian), and its palaeographic range to West Gondwana. Currently under study, this relatively common component of the lower Fezouata Shale fauna is only briefly discussed. Features characterizing the genus Thelxiope and its components almost exclusively pertain to the sagittal spines, for the scarcity and inconsistent preservation of the Cambrian materials as-yet available preclude a confident assessment of the variability of other morphological features. The pygidium in Thelxiope and Mollisonia is not composed of four, but three tergites essentially similar to thoracic ones, except for the lack of articulations.

The Drumian Wheeler Formation preserves one of the most diverse exceptionally preserved faunas of the Cambrian period. Here we describe Messorocaris magna gen. et sp. nov., a new non-biomineralizing arthropod from this formation tentatively assigned to the family Sanctacarididae. The new taxon exhibits a vaulted axial region, and wide pleural regions forming sickle-shaped lateral extensions in the trunk, a character particularly distinctive within the Sanctacarididae. This description provides an opportunity to stress the fact that the ‘Wheeler fauna’ encompasses two distinct assemblages, as confirmed by similarity analysis. These contemporaneous faunas lived at different bathymetries, and should be treated as separate entities.

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