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Port Jackson shark

Port Jackson shark

The Port Jackson shark, Heterodontus portusjacksoni, is a type of bullhead shark of the family Heterodontidae, found in the coastal region of southern Australia, including the waters off Port Jackson. It has a large head with prominent forehead ridges and dark brown harness-like markings on a lighter grey-brown body. Port Jackson sharks can grow up to 5.5 ft (1.67 m) long.

The Port Jackson shark is a migratory species, travelling south in the summer and returning north to breed in the winter months. They feed on hard-shelled mollusks, crustaceans, sea urchins, and fish.

Respiratory system

The Port Jackson shark has five gills, the first supports only a single row of gill filaments, while the remaining four support double rows of filaments. Each of the second to the fifth gill arches supports a sheet of muscular and connective tissue called a septum. The shark possesses behind each eye an accessory respiratory organ called a spiracle. Along the top and bottom of each gill filament are delicate, closely-packed, transverse flaps of gill tissue known as secondary lamellae. It is these lamellae that are the actual sites of gas exchange. Each lamella is equipped with tiny arteries that carry blood in a direction opposite to that of the water flowing over them. To compensate for the relatively low concentration of dissolved oxygen in seawater, water passes over the secondary lamellae of sharks some 20 times more slowly than air remains in contact with the equivalent gas exchange sites, such as the alveoli of the lungs found in humans. This delay allows sufficient time for dissolved oxygen to diffuse into a shark's blood.

Port Jackson sharks have the ability to eat and breathe at the same time. This ability is unusual for sharks which mostly need to swim with the mouth open to force water over the gills. The Port Jackson shark can pump water into the first enlarged gill slit and out through the other four gill slits. By pumping water across the gills, the shark does not need to move to breathe. It can lie on the bottom for long periods of time.

Reproductive system

The Port Jackson shark usually breeds in late winter and early spring. This is when large numbers of them lay on the bottom under ledges and in caves. They usually return to the same area every winter to breed, and this is often the same gullies or the same caves. Port Jackson sharks usually migrate up to 800 km north in the summer, and will migrate back north for the winter. They lay about 15 corkscrew-shaped eggs, which they wedge into rock crevices and among kelp. Their eggs are tough, dark coloured, spiral looking, about 7 or 8 [centimetre|cm]] wide and about 15 cm long. They are usually soft when laid and become harder afterwards; they take about 10 to 12 months to hatch. After hatching the young sharks are on their own. Males become sexually mature around 8 to 10 years of age and females around 11 to 14 years of age.

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.

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