Feeding and Digestion in the Aberrant Planarian Bdellasimilis Barwicki (Turbellaria: Tricladida: Procerodidae): an Ectosymbiote of Freshwater Turtles in Queensland and New South Wales.

Abstract

Bdellasimilis barwicki is an aberrant planarian, from a predominantly free-living marine family, inhabiting the limb pits of freshwater turtles in Queensland and New South Wales. It appears to feed mainly as an ectosymbiotic predator on aquatic oligochaetes and insect larvae, but laboratory observations suggest that it may also be an opportunistic commensal ingesting accidentally discarded portions of the host's food. The feeding mechanism is unique amongst triclad turbellarians in that food is taken intact into the peripharyngeal chamber, which is capable of very great expansion, and held there while the cylindrical plicate pharynx penetrates it to withdraw fragments piecemeal into the intestine. Intestinal structure is essentially the same as in other triclads, the monolayered gastrodermis being differentiated into gland cells and columnar phagocytes. Digestion, too; follows the characteristic triclad pattern; acidic proteolysis initiated in the gut lumen by endopeptidases from the gland cells is followed by phagocytosis and completion of digestion within the columnar cells by intracellular enzymes of which endopeptidases, arylamidases, and acid and alkaline phosphatases have been demonstrated histochemically. Large deposits of lipid occur in the gastrodermis, mesenchyme and vitellaria, but glycogen is found in only small amounts at these sites and in the musculature, testes and ovaries. The brain and principal longitudinal nerve cords contain large quantities of acetylcholinesterase, arylamidases and alkaline phosphatase.