The rhynchocoelan Lineus ruber feeds on small annelids and crustaceans which are captured by the unarmed proboscis and swallowed whole.2. The alimentary canal is differentiated into three regions: a buccal cavity, a foregut where the prey is killed by acid secretions, and an intestine where it is digested.
3. Digestion is the result of both extracellular and intracellular processes and occurs in an acid medium of pH 5.0-5.5. The enzymes responsible for the initial extracellular breakdown come from gland cells in the intestinal wall and digestion is completed within the columnar cells of the latter. Semidigested food enters these columnar cells by a phagocytic process and this involves temporary modifications in the form and function of their cilia.
4. The food reserves consist of fat deposits in the parenchyma and, to a lesser extent, in the columnar cells of the intestine.
