Figure 1.

The tropical abalone as a model for understanding molluskan biomineralization. (a) Juvenile shell pigmentation follows a simple set of rules; dots are blue when in a red field (*) and orange when in a cream field (†). (b) The decalcified shell reveals a blue color within previous red fields (*). (c) SEM reveals the topographic shell pattern with a ridge (r) and valley (v) organization, and regularly spaced respiratory pores (white arrows). Shells in (a-c) are 5 mm. (d) Pigmentation is restricted to the outer periostracum (Pe), which overlies the protein matrix (Pm). The mantle (Mt) continuously secretes these structures. Insert, SEM cross section of the shell, revealing the calcitic prismatic layer (c/pr) and the inner aragonitic nacreous layer (a/nc). (e) The leading edge of the mantle (dorsal view, anterior top) consists of two folds. Between the ventral most inner (if) and outer folds (of) lies the periostracal groove (§). At the anterior edge of the outer fold there is a crease in the epithelium (arrow). SEM insert of the same region. (f) Section through the mantle edge (dorsal top, anterior right) highlighting the periostracal groove (§). (g) TEM of solid boxed section in (f) reveals light (Lc) and dark (Dc) staining secretory cell types, with microvilli (Mv). (h) TEM section of dashed box in (f) reveals the brush border-like lining of this crease (large arrowhead). Secreted extracellular material (arrows) is evident. Inset shows this extracellular material (white arrowhead) possibly responsible for the initiation of calcification. Scale bars: (e, f) 50 μm; (g, h) 5 μm.