Port Jackson Shark - Digestive System

Digestive System

Digestion of food can take a long time in the Port Jackson shark. Food moves from the mouth to the 'J' shaped stomach, where it is stored and initial digestion occurs. Unwanted items may never get any further than the stomach, and are coughed up again. They have the ability to turn their stomachs inside out and spit it out of their mouths in order to get rid of any unwanted contents. One of the biggest differences in digestion in the shark when compared to mammals is the extremely short intestine. This short length is achieved by the spiral valve with multiple turns within a single short section instead of a very long tube-like intestine. The valve provides a very long surface area for the digestion of food, requiring it to pass around inside the apparently short gut until fully digested, when remaining waste products pass by. The most obvious internal organ in sharks is the huge liver, which often fills most of the body cavity. Dietary items include sea urchins, molluscs, crustaceans and fishes. Black sea urchins, Centrostephanus rodgersi are often eaten. Port Jackson Sharks forage for food at night when their prey are most active. They often use caves and rocky outcrops as protection during the day. When most people think of shark teeth, they think of large, sharp teeth like those in the film 'Jaws'. Not all sharks have teeth like these. The teeth of the Port Jackson Shark are very different. They are not serrated, and the front teeth have a very different shape from those found at the back of the jaws, hence the genus name Heterodontus (from the Greek heteros, meaning 'different', and dont, meaning 'tooth'). The anterior teeth are small and pointed, whereas the posterior teeth are broad and flat. The teeth function to hold and break, then crush and grind the shells of molluscs and echinoderms. Juvenile Port Jackson Sharks have more pointed teeth and feed on a higher proportion of soft-bodied prey than adults. They can feed by sucking in water and sand from the bottom, blowing the sand out of the gill slits, and retaining the food, which is swallowed.