Whitney Mantooth Dissection of the Spiny DogfishWhen thinking of a shark, most people think of being attacked in the ocean. However, people are hardly ever actually attacked by sharks. When in fact, most sharks only attack humans because they mistake them for a seal or a fish. One shark which is abundant in population, and not seen as a threat to humans is the, spiny dogfish shark. The spiny dogfish shark, squalus acanthias, is abundant in population. Fishermen called the shark a dogfish because it exhibits a trait that is identified with wolves: hunting in packs. The dogfish is used commonly for human consumption, soil fertilizer, pet food, in laboratories, and as olive oil. This shark is also known as the skittledog, spotted dogfish,2 Spiny Dogfishwhite-spotted dogfish, codshark, piked dogfish, and thorndog. The name spiny dogfish comes from the shark’s venomous spines it has on each dorsal fin. Class of the Spiny dogfishAppearanceThe dogfish’s appearance has a gray body with white on the underbelly. It also has white spots around the body, randomly placed (Smith, 1998). The dogfish has a short snout, nostril, mouth, gills, and large eyes. Also, it has two dorsal fins with mildly poisonous spines before the dorsal fins. The two dorsal fins are spaced out, the first one is near the middle of the body, and the second near the tail. The tail is called the caudal fin, and each fin on the side of the fish is known as a pectoral fin (Smith, 1998). They alsohave a pelvic fin, and whether it is a male of female, it might have claspers (male). The Kingdom Animalia (animals)Phylum ChordataSubPhylum Vertebrata (vertebrates)Class Chondrichthyes (cartilaginous fish)Subclass Elasmobranchii (sharks and rays)Order Squaliformes (dogfish sharks)Family SqualidaeGenus SqualusSpecies acanthias(Enchanted Learning, 2010)Whitney Mantooth dogfish averages between three and four feet long (University of Miami, 2000). It is also estimated that the dogfish can live anywhere from 25 to 100 years.Support StructureUnlike most vertebrates, a shark does not have a bony skeleton, but instead a skeleton made up of cartilage. Fins, pelvic girdle, nasal capsule, and other skeletal parts are composed of cartilage (University of Miami, 2000). The shark is also composed of muscles. It has myotomes which are segments of muscles that line the body from the trunk to the tail, and have a zig-zag pattern. On the dorsal side are Epaxial muscles; Hypaxial muscles are located below the Epaxial muscles (University of Miami, 2000). The Preorbitalis helps to open the mouth, and is located ventral from the eye. Adductor muscles, which are caudal from the eye help, close the mouth (University of Miami, 2000). The Levator Palatoquadrati controls the jaw, and help raise the jaw. The muscle that helps close the jaw is called the Levator Hyomandibulae (University of Miami, 2000). Ventral Constrictors, Dorsal Constrictors, and the Septal Constrictors help2 Spiny Dogfishconstrict the gills (University of Miami, 2000). Located on the dorsal pectoral fin, the Pectoral Levators raise the fin. The Cucullaris moves the pectoral fin dorsally and cranially (University of Miami, 2000).DigestionThe pleuroperitoneal cavity holds the pancreas, gall bladder, stomach and pancrease; this cavity helps protect the organs (University of Miami, 2000). The liver is made of three lobes, the smaller lobe holds the glass bladder which houses bile produced from the liver. Food first enters the body through the mouth which it enters the esophagus, and the food is pushed down the esophagus by the esophageal papillae, and once down it enters the stomach (University of Miami, 2000). The stomach is J-shaped and is used in digestion. The stomach has a pyloric sphincter, which is a muscular ring that opens and closes the stomach from the intestines (University of Miami, 2000). The stomach is followed by the duodenum, which receives bile from the gall bladder to help break down and process nutrients and food. After the duodenum is the Ilium and spiral valve, which absorb more nutrients, B12 and bile salts (University of Miami, 2000). Next, the colon absorbs water and salts from the food, before it goes to the rectum. The rectal gland controls salts and releases it into the rectum to await exit (University of Miami, 2000). Finally the rectum stores waste that was not absorbed, or could not be absorbed to await exit out of cloaca.Reproductive StructureSexual organs of the dogfish include the uterus, testes, ovaries, claspers, and cloaca. The spiny dogfish has a uterus that holds and stores the developing eggs (University of Miami, 2000). The testes are oval shaped and produce male gametes, in aWhitney Mantooth male shark. Ovaries are cream colored and store the eggs in the female. The claspers are finger-like and assist in mating in males (University of Miami, 2000). The only opening in the digestive tract and means for sexual reproduction is the cloaca. Respiratory SystemJust like most mammals, sharks have a repiratory system, which includes a heart and lungs. However, since the shark is completely submerged in water, it needs special organs to pull the oxygen out of the water (University of Miami, 2000). The respiratory system of the spiny dogfish consists of a pericardial cavity, heart, efferent brachial arteries, atrium, gill rakers, ventricle, gill arches, spiracles, and gill slits. The pericardial cavity protects the heart and branching arteries. The heart is a specialized muscle that has two halves; atrium and ventricles (University of Miami, 2000). The atrium forces blood into the ventricles, and from there the ventricle push the blood to the rest of the body. Blood is pumped to and from the fins by the efferent brachial arteries (University of Miami, 2000). Gill rakers help the gills take in more oxygen by increasing surface area. Water is allowed to exit the gills of the dogfish after passing over, by the gill slits. Spiracles, located on the head, allow for water to pass through the gills even when the mouth is closed (University of Miami, 2000). The spleen also aids in regulate blood flow, and cleans the body from toxins and helps circulation of blood.DetectionMany sharks are able to detect disturbances in the water, and this helps them find prey and even other sharks. The organs to help in detection include the nares, Ampullae of Lorenzini, and the lateral line (University of Miami, 2000). Nares are used to detect chemicals in the water, this