The epidermis cells of mandible teeth in the terrestrial isopod Porcellio scaber: Differentiations for mineralisation with calcium phosphate and carbonate

Abstract

Generally, the mineralisation of the crustacean cuticle occurs when the cuticle has expanded after moulting. However, in the partes incisivae of Porcellio scaber, cuticle mineralisation with calcium phosphate already occurs before the moult. We investigated the ultrastructure and distribution of organelles within the epidermis cells and searched for calcium-containing organelles using EDX and EFTEM analysis. We found two different cell types. Calcium carbonate-secreting C-cells, which resemble the epithelial cells of the general integument, and the P-cells, which, as an unusual feature, have cell extensions up to 400 μm long. During secretion of the partes incisivae, these extensions end at the unmineralised tip and the phosphate-containing middle region. Their cell bodies contain most of the mitochondria located in basal folds and a high amount of endoplasmic reticulum. The cell extensions contain many microtubules, endoplasmic reticulum, large and small vesicles and densely stained rod-shaped cisternae. The rod-shaped cisternae and the endoplasmic reticulum contain calcium. During cuticle mineralisation, vesicles, which probably belong to the endo-lysosomal system, contain calcium and phosphorus. They occur at some distance and close to the cuticle. The mineral in these vesicles has a similar composition to that within the cuticle, suggesting that they play a role in cuticle mineralisation.