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The morphology and histology of the alimentary canal of the rock chiton Acanthopleura spinigera are described and the ability of regions of the gut to digest specific substrates investigated. The oesophagus is produced into a pair of thin-walled lateral pouches, the salivary glands or “sugar glands” which empty into the stomach. Folds of the capacious stomach are almost obscured by the large digestive gland over which is coiled the intestine. Histologically the gut consists of an outer layer of connective tissue, an inner muscular layer and a ciliated epithelium which varies in thickness from one region to the next. Proteases are most active in the stomach, digestive gland and anterior intestine at pH 6·5 and in the posterior intestine at pH 7·5-8·5. The digestion of lipoidal substance was greatest in the stomach and digestive gland and least in anterior intestine. There was little increase in the amount of digestion product obtained after 20 hours incubation. All regions of the alimentary canal and salivary gland were capable of digesting carbohydrates except that many low molecular weight carbohydrates were digested by salivary gland extracts only. The amylases were most active at pH 6–6·5. It is concluded that digestive enzymes are distributed throughout the intestinal tract but the amount of enzyme present varies from region to region, and is greatest just after feeding.