Shark External Anatomy
Instruction
Be sure to write about what you are learning in the lab section of your notebook. You will be expected to answer questions about the lab activity during the lab self test and lab quiz. It helps to have your text and coloring books open beside you for support.
| Refer to the Assigned Readings Below: | |
| Marine Biology Textbook | Chapter 8, pages 155 to 157 and 161 to 162 |
| Marine Biology Coloring Book | Plates 49 to 51 |
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The shark has a graceful and streamlined body shape built for fast, long-distance swimming. The body is divided into the head, trunk, and tail. The shark's body is dark gray above and almost white below. Along the sides of the body is a light-colored horizontal stripe called the lateral line. The line is made up of a series of tiny pores that lead to receptors that are sensitive to the mechanical movement of water and to sudden changes of pressure. The spiny dogfish has a double dorsal fin. The anterior dorsal fin is larger than the posterior dorsal fin. The spiny dogfish has the presence two spines, one immediately in front of each dorsal fin. The spines carry a poison secreted by glands at their base. The caudal fin is divided into two lobes: a larger dorsal lobe and a smaller ventral lobe. This type of tail is known as a heterocercal tail. |
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The rostrum is the pointed snout at the anterior end. This tapered tip at the anterior end helps overcome water resistance in swimming. The eyes are prominent in sharks and are very similar to the eyes of man. A transparent cornea covers and protects the eye. A darkly pigmented iris can be seen below the cornea with the pupil at its center. Upper and lower eyelids protect the eye. Just inside the lower lid is a membrane that extends over the surface of the eye to cover the cornea. Large spiracle openings are located posterior and dorsal to the eyes. A spiracular valve permits the opening and closing of the external spiracular pore. The spiracle is an incurrent water passageway leading into the mouth for respiration. Most sharks have five external gill slits located on their sides, behind the mouth and in front of the pectoral fins. Water taken in by the mouth and spiracles is passed over the internal gills and forced out by way of the gill slits.
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The paired pectoral fins act like an airplane's wings to provide the lift needed to keep the shark from sinking. The paired pelvic fins are located on either side of the cloacal aperture. They are different in males and females. |
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The opening to the
mouth of sharks is always on the underside. The teeth are
sharp and pointed. There are several rows of flattened teeth lying
behind the upright set ready to replace them when worn out or lost. The external nares,
or external nostrils are located on the underside (ventral surface)
of the rostrum anterior to the jaws. A nasal flap separates the
incurrent from the excurrent opening. Water passes into and out
of the olfactory sac, permitting the shark to detect the odors in
the water. The patches of pores on the head in the areas of the eyes, snout, and nostrils are the openings of the ampullae of Lorenzini. These sense organs are sensitive to changes in temperature, water pressure, electrical fields, and salinity. |
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Males have stout, grooved copulatory organs called claspers on the inner side of their pelvic fins. Fertilization in the dogfish shark is internal. During copulation, one of the claspers is inserted into the oviduct orifice of the female. The sperm proceed from the cloaca of the male along the groove on the dorsal surface of the clasper into the female. The cloaca receives the products of the intestine, the urinary, and the genital ducts. The name cloaca, meaning sewer, seems quite appropriate. |
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The cloacal opening is located on the ventral surface between the pelvic fins. |
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The muscles revealed by skinning the side of the shark are arranged in W-shaped bundles called myomeres. The myomeres are separated from one another by connective tissue. Contractions of the myomeres produce the side-to-side motion that propels the shark foward. |
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Lab Activity 5.2 Shark Digestive Anatomy