Figure 5: SEM views of semidecalcified fractures of the shells of the Cavolinioidea.

(a) Cavolinia longirostris, showing the network of organic threads left after decalcification. (b) Cuvierina columnella. Long organic thread (>20 μm long, total length not shown) crossing a semidecalcified fibre through its external part (arrows). (c) Cuvierina columnella. Arrows point to organic fibres that have remained more or less in situ; they consistently enter the corresponding fibres close to their external surfaces. (d) Specimen of Cavolinia longirostris in which the dissolution has not completely exposed the organic fibres, which are still surrounded by calcium carbonate granules. They appear as flexible thin extensions of the top parts of the mineral fibres, which have deflected leftwards during the treatment (some cases are indicated with arrows). The inset is a detail. (a,d) are views of the surfaces of the fibres looking towards the external shell surface. (b,c) are lateral views with the external shell surface to the top.