Australian Cainozoic Bryozoa, 1: Nudicella gen. nov. (Onychocellidae,Cheilostomata): taxonomy,palaeoenvironments and biogeography

The new bryozoan genus Nudicella (Onychocellidae, Cheilostomata) is proposed to accommodate the common and widespread Australian Cainozoic cheilostome bryozoan Eschara clarkei Tenison Woods, which is redescribed and subdivided into four species: N. clarkei (Tenison Woods), N. cribriforma sp. nov., N. latiramosa sp. nov. and N. tenuis sp. nov. Cellaria gigantea Maplestone is also reassigned to Nudicella. Colonies of this genus display a wide variety of growth forms, including cribrate fenestrate, flat robust branching, foliose, delicate branching and encrusting; their occurrences correlate with changes in sedimentary facies and palaeoenvironments. The distinctive cribrate style of fenestrate growth form has evolved convergently in unrelated bryozoan groups at various geological intervals. It is found in a wide variety of sedimentary facies, as in other coexisting opportunistic genera such as Celleporaria, indicating a wide ecological tolerance. The oldest recorded occurrence of Nudicella is in the Paleocene of north western Australia. From there it appears to spread south in the Eocene and then east towards the Otway Basin in southeastern Australia, where it occurs in the Oligocene and Miocene; no post-Miocene representatives of this genus are yet known.