Hannaea inaequidentata, dividing half mother frustule, external view, SEM 97 slightly displaced half mother frustule, note its rounded outline 98 middle detail of Fig. 97 showing broken longitudinal perizonium 99, 100 details of Fig. 98 (two asterisks) showing broken longitudinal perizonium (arrows) and distinctive plaques (arrowheads) 101 apex detail of Fig. 97 showing irregular ocellulimbus and 4:2 configuration of girdle bands 102 another apex detail of Fig. 97 showing 4:2 configuration of girdle bands and a new-born hypovalve with regular sternum (two arrows). Scale bars: 10 μm (97, 98), 2 μm (99–102).