Shark (Selachimorpha)
Classification: Chondrichthyes Class of Chordate Phylum
Overview
Sharks have been around for hundreds of millions of years. There are over 500 species of sharks swimming in the world's oceans. They range in size from the length of a human hand to an astounding 39 feet long. Sharks are known for their heightened senses, such as smell and hearing, and even a sixth-sense. People have become so fascinated by these creatures that the Discovery Channel has dedicated a week to these mammals, widely known as Shark Week.
Dissection Procedure
The first step in dissecting a Dogfish shark is studying the external anatomy. The external anatomy includes the different fins, rostrum, nostrils, eyes, mouth, and gills. The next step is dissecting the digestive anatomy. From the incision you will be able to see peritoneum, the liver, and the gall bladder. In moving the liver aside, you will see the esophagus and stomach, and also the pancreas, spleen, and intestine. Moving the intestine aside you will see the colon, rectal gland, and the cloaca. The next step is dissecting the circulatory anatomy of the dogfish shark. By removing the skin and some of the ventral muscle, you will expose the atrium, the ventricle, and the pericardial cavity. You will then examine the ventral aorta, the dorsal aorta, and the arteries. The next step is the dissection of the urogenital anatomy. By removing the liver, pancreas, and spleen; you reveal the gonads, kidneys, and associated ducts. The last dissection will be of the shark's nervous system. By removing the skin from the dorsal surface the cranial cavity and brain are exposed. You will see the cerebellum, cerebral, medulla, the optic lobe, and the spinal cord, along with different nerves also.
Nervous System
The nervous system functions in communication between various parts of an organism, and between the organism and its external environment. The nervous system consists of the central nervous system; the brain and spinal cord, and the peripheral nervous system; the sense organs, cranial and spinal nerves and their branches.
External Anatomy
Sharks have skeletons made of cartilage, which allows sharks to stay afloat and swim long distances without getting tired. Every shark also has several rows of teeth lining its jaws. They are constantly loosing and shredding teeth. Sharks have an array of gill slits. The shark's skin feels like sandpaper because of the placoid scales that make up the skin.
Dogfish Shark External Anatomy
Respiratory System
Sharks, like other fish, use gills to breathe. There are usually between 5 and 7 gill slits. Water enters the mouth of the shark, enters a canal between the mouth and the gills called the orobranchial cavity, and then passes back to the outside through the gill openings. As water passes over the gills, oxygen is absorbed into the blood across the think skin of gill surface and carbon dioxide is omitted into the water.
Digestive System
Most sharks swallow their food whole or in very large pieces. Food goes down the esophagus. Sharks have a U shaped stomach that uses very strong stomach acids and enzymes to dissolve what the shark eats. The stomach then leads to the intestines and the digestive tract, which then leads to the rectum and cloaca.
Skeletal System
Unlike terrestrial animals, humans, and even other marine life, sharks skeletons are made purely of cartilage and connective tissue or muscle. There is no bone. The skull is also made from cartilage.