Calcium Detection and Other Cellular Studies in the Esophagus and Crop of the Marine Slug Aglaja tricolorata (Euopisthobranchia, Cephalaspidea)
2014
Lobo-da-Cunha, Alexandre | Pereira-Sousa, Joana | Oliveira, Elsa | Alves, Angela | Guimarães, Fernanda | Calado, Gonçalo
To obtain more data about the digestive system of cephalaspideans, the esophagus and crop of Aglaja tricolorata were investigated using light and electron microscopy. In this cephalaspidean, the low epithelial cells of the anterior esophagus have a border of microvilli covered by a cuticle formed by acid polysaccharides. The esophageal pouches at the hind region of the anterior esophagus contain subepithelial secretory cells filled with electron-dense vesicles rich in neutral polysaccharides and proteins. A ciliated epithelium covers the base of the esophageal pouches. In the crop, the tall columnar epithelium is covered by a cuticle and forms many deep invaginations. The cuticle on the surface of the epithelium contains acid polysaccharides, but the material filling the lumen of the epithelial invaginations consists of neutral polysaccharides and proteins. Epithelial cells of the crop have a border of short microvilli and many mitochondria; lysosome-like bodies and some lipid droplets are present in the apical region. The elongated nucleus, numerous deep cell membrane invaginations and several hemidesmosomes are located at the basal region. Secretory cells are absent in the crop. Numerous large vacuolar cells are present in the connective tissue of the crop. With the pyroantimonate method, calcium was detected in the peripheral vesicles and central vacuole of these cells. WDS X-ray Intensity maps obtained by EPMA (Electron microprobe) confirmed the presence of calcium. This result supports the relationship between the vacuolar cells of aglajids and the calcium cells of pulmonate gastropods. In the posterior esophagus, epithelial cells are similar to the epithelial cells of the crop and secretory cells are also absent.
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