Descriptions are given of seven Antarctic species of cyclostome bryozoans belonging to the genera Idmidronea and Exidmonea, of which I. fraudulenta, I. pellucida and E. arcuata are new. The gonozooids of I. pseudocrisina Borg are described for the first time, and all species are newly illustrated using SEM. The large sample size available has permitted particular attention to be given to intraspecific variability, especially of the ooeciostome which is shown to be more variable than has been previously acknowledged.