Histochemical and ultrastructural study of the alimentary tract of the freshwater snail Lymnaea stagnalis

Abstract

The alimentary tract of the freshwater snail Lymnaea stagnalis, except the salivary glands and the digestive gland, was studied with histochemical and ultrastructural methods. The main focus was on the epithelia. Previous studies have indicated that the digestive gland, where intracellular digestion occurs, plays the major role in the digestion process. The main cell types of the tract are ciliated cells and cells with microvilli. The presence of ciliated cells reflects transport of food particles and faeces. In particular areas, viz. the prooesophagus and the pylorus, the epithelium is almost exclusively composed of ciliated cells. Both cell types show signs of endocytosis, lysosomal breakdown of substances, and storage of reserve materials (glycogen, lipid, protein). These features are very prominent in the crop and in the first part of the prointestine and they would indicate that absorption of energy-rich substances can occur in the whole tract. Ten types of gland cells were distinguished. Their possible functions are discussed on the basis of their histochemical properties and ultrastructure of the secretion products. The observations suggest that some of the cell types produce two different substances, one of which may have enzymatic properties. The epithelium of the gizzard consists of cells possessing stout microvilli, which extend into a special coating produced by these cells. The morphology of the epithelium reflects the function of the gizzard, which is comminution of food particles. In the mid- and postintestine occur areas composed of villi cells that possess an extensive basal labyrinth. The morphology of the cells indicates that they may be involved in absorption of water and ions from the faecal pellets. The whole tract is richly innervated. Numerous neurons occur in the connective tissue and muscle layers. Furthermore, in several areas numerous intraepithelial neurons were observed.

Elimination of the Cyanobacterial Hepatotoxin Microcystin from the freshwater Pulmonate Snail Lymnaea stagnalis jugularis (SAY)

“…The digestive gland has significant capacity to assimilate (primarily via cellular uptake) dissolved and particulate nutrients and compounds (Carriker, 1946;Boer & Kits, 1990). Our detection of toxin in snails beyond 8 h corresponds favorably with Veldhuijzen (1974), who demonstrated that fine and soluble digestible matter assimilated by digestive gland cells might remain detectable for at least 100 h postingestion.…”

“…Findings on gross morphological, ultrastructural and histochemical aspects (Carriker, 1946;Boer & Kits, 1990) and particle sorting and retention time (Veldhuijzen, 1974) within the alimentary tract of Lymnaea are summarized in Table 2. Coarse, indigestible plant matter passes from the gizzard into the pylorus, where ciliary sorting of food particles by size and digestibility occurs.…”

Oral water ingestion in the pulmonate freshwater snail,Lymnaea stagnalis

“…stagnalis seems well equipped to serve this function. Especially the mid-and post-intestine contain areas showing all morphological characteristics of water-and salttransporting epithelia (Boer and Kits 1990).…”

“…This procedure was adopted since it was impossible (within a reasonable period of time) to dissect out the complete digestive system without damaging it. The first part, ''digestive gland'', contained the digestive gland (carrying the largest lumen of the alimentary system; supposed to contain almost all radioactivity), the post-oesophagus, the crop and the gizzard, the pylorus and the vestibulum, the pro-intestine, mid-intestine and the largest part of the post-intestine (Boer and Kits 1990). Besides the ovotestis and its duct, no other organs were present in this fraction.…”

Applications of Lectins and Neoglycoconjugates in Histology and Pathology

“…Basic reagents commonly used included Alcian blue, azure A, and other thiazines such as thionin and toluidine blue, aldehyde fuchsin and iron diamines [Spicer and Schulte, 1992;Yamada, 1993;Schumacher and Adam, 1994]. These conventional methods alone [Bremer, 1987;Gilks et al, 1988;Boer and Kits, 1990;Chieffi-Baccari et al, 1990;Gonzalez de Canales et al, 1992;Saint-Girons and Zylberberg, 1992] or in combination with lectins [Danguy andGenten, 1989, 1990;Genten and Danguy, 1990a-c;Castells et al, 1991;Getchell and Mellert, 1991;Sharma and Schumacher, 1992;Uhr et al, 1993] have successfully been employed as reported in the given selection of recent papers of glycan histochemistry.…”