Histochemical and ultrastructural studies on the salivary glands of Helix aspersa (Mollusca)

Abstract

A histochemical and ultrastructural study was carried out on the salivary glands of adult specimens of Helix aspersa. Histochemically four cell types were distinguished: mucocyte I, mucocyte II, pseudochromosome cell and protein cell. The first secretes neutral and acid mucins. Mucocyte II and pseudochromosome cells produce acid mucins and the protein cell secretes neutral mucins and proteins. The ultrastructural data for differentiating these four cell types is discussed. Mucocytes I have a characteristic arrangement of rough endoplasmatic reticulum and basal infoldings. Mucocytes II have pseudocrystalline formations in the rough endoplasmatic reticulum and intraluminary ducts. Pseudochromosome cells have typical granules with a reticular central zone. Protein cells have serous homogenous secretion. The epithelium of the salivary ducts is described.

Histology and ultrastructure of the salivary glands in Bulla striata (Mollusca, Opisthobranchia)

“…In the salivary glands of A. depilans , the mature granular cells possess electron‐dense secretory granules containing high amounts of proteins associated with neutral polysaccharides (Lobo‐da‐Cunha 2001), but similar cells were not detected in the salivary glands of B. striata . The salivary glands of pulmonate gastropods also contain cells with electron‐dense granules containing proteins and neutral polysaccharides, like the grain cells of Deroceras reticulatum (= Agriolimax reticulatus ) (Walker 1970), and the protein cells of Helix aspersa (Moreno et al 1982). This group could also include the P1 cells of Arion ater (Moya et al 1992), type IV cells of L. maximus (Beltz & Gelperin 1979), and the basophilous cells described by Serrano et al (1996) in four species of terrestrial pulmonate gastropods, although histochemical studies of the secretion were not conducted in these species.…”

“…The alveolar cells described in the salivary glands of several species of pulmonates (Serrano et al 1996) resembled the vacuolated cells, but their secretory vesicles have a higher electron density and they can be stained with conventional light microscopical methods. The cell type III in L. maximus (Beltz & Gelperin 1979), mucocytes I in H. aspersa (Moreno et al 1982), and P2 cells in A. ater (Moya et al 1992) are examples of other cells that seem to belong to the alveolar type. According to the morphological data, the vacuolated and alveolar cells could be considered as closely related cell types.…”

“…Moreover, in some vacuolated cells in A. depilans and B. striata , vesicles with different electron densities co‐exist, reinforcing the similarity between those two cell types. In the salivary glands of H. aspersa , proteins, acidic mucosubstances, and PAS‐positive materials were detected in secretory cells corresponding to the alveolar type (Moreno et al 1982; Charrier 1988). In the vacuolated cells in A. depilans and B. striata , a few vacuoles also contained PAS‐positive materials, and acidic mucopolysaccharides are present.…”

“…In the pulmonates Eobania vermiculata and H. aspersa , cilia were not observed in the ducts of the salivary glands, whatever their diameter. Thus, in these cases, the flow of secretion must depend only on the contraction of the muscle cells (Moreno et al 1982; Bani et al 1990). The opposite situation can be found in Lymnaea stagnalis , in which the movement of saliva seems to result from ciliary action alone (Boer et al 1967).…”

“…The main salivary ducts of terrestrial pulmonate gastropods are lined by epithelial cells with a large number of very deep infolds of the basal cell membrane. These cells also contain a well‐developed border of microvilli, and many mitochondria are present between the membrane folds, suggesting a role in water and ion transport (Walker 1970; Beltz & Gelperin 1979; Moreno et al 1982). On the other hand, these aspects were not found in the salivary ducts of L. stagnalis , a freshwater pulmonate (Boer et al 1967), in A. depilans (Lobo‐da‐Cunha 2001), or B. striata .…”