Bryozoan frontal shields: the type species of Desmacystis, Rhamphostomella, Rhamphosmittina, Rhamphostomellina, and new genus Arctonula

Frontal shields have been examined in the type species of several genera of ascophorine cheilostomates. Desmacystis (Desmacystidae) is not an'anascan'as previously thought, but has a cryptocystal shield which is here interpreted to be derived from an umbonuloid shield by foreshortening, possibly from a rhamphostomellan ancestor. Rhamphostomella (type species Rscabra ) and Rhamphosmittina (type species R. bassleero ) (both in the family Porellidae Vigneaux, here raised from subfamily rank) also have umbonuloid shields. Arctomula , new genus, is established for Lepralia arctica M. Sars and transferred from the Umbonulidae to the Exochellidac. Rhamphostomellina (type species R. posidoniue ) has a lepralioid shield. It is here included in the family Celleporidae.