The record of cavity-dwelling organisms (coelobionts) is long ranging, and is known to extend as far back as the upper Lower Cambrian. Older coelobionts, from the middle Lower Cambrian Poleta Formation of western Nevada, have been found, however, in framework cavities in archaeocyathid patch reefs, thus extending the record of the coelobiontic community even further.The Poleta Formation coelobiontic community is less diverse than that found in the upper Lower Cambrian community (from cavities in archaeocyathid patch reefs of the Forteau Formation of Labrador); it is dominated by algae, in particular Epiphyton. Renalcis and encrusting mammillary algae play a secondary role. Juvenile archaeocyathids, soft sponges, Archaeotrypa, and microtubules make up the remainder of the skeletal cavity biota. Sediments that floor the cavities contain a low-diversity but abundant infauna represented by meandering burrows; horizontal feeding or locomotion traces were produced on the surface of the cavity sediments.