Figure 3: Features on the internal shell (growth) surface of the Cavolinioidea as revealed by SEM.

(a–c) Slightly bleached specimens of Cuvierina columnella (a,b), and Cuvierina urceolaris (c), showing frequent examples of changes in orientation of the fibres (some trajectories are indicated with arrows in (a,c)), fibre interception and reappearance (partly broken arrows in (a,c)), and fibre division (coarse arrow in (a) and splitting arrows in (b)). (d) Cavolinia inflexa. Several tips are in the process of division (arrows). Note also the linear or angular anterior outline of the tips. (e) Oblique close-up view of Cuvierina columnella. Some tips (black arrows) have a planar adoral slope (black arrows). White arrows point to missing tips. (f) Heavily bleached shell of Cuvierina columnella. The tips of all fibres have dissolved preferentially. The close-up view (inset) shows how the dissolution has penetrated inwards towards the shell interior.