Variability in the shape and position of the ooeciostome in Antarctic idmidroniform cyclostome bryozoans is described in detail. All characters analysed (size and shape of ooeciostome and ooeciopore, ooeciostome position, orientation of ooeciopore) exhibit variability. Therefore, they may be categorized as useful rather than diagnostic taxonomic characters. Recent idmidroniform bryozoans are arranged in a morphoseries reflecting some possible stages in the evolution of the ooeciostome. Possible trends include loss of terminal position, length decrease, increased curvature and flattening. The ooeciostome of Idmidronea fraudulenta Ostrovsky & Taylor, 1996 is studied by SEM for the first time.