Activity 1: External Anatomy
Click on any photograph for an enlarged view in a separate window.
Click HERE to access the Activity 1 Dissection Booklet
Click HERE to view the Shark Dissection Video Part 1
Examine the side view photographs of the spiny dogfish shark by clicking the blue lettered links in the column to the right.
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 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.
Examine the anterior view photographs of the shark by clicking the blue lettered links in the column to the right.
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 thire 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.
Examine the bottom view photographs of the shark by clicking the blue lettered links in the column to the right.
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.
Examine the photographs of the shark's snout by clicking the blue lettered links in the column to the right.
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 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 of 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.
Examine the photographs of the male shark's pelvic region by clicking the blue lettered links in the column to the right.
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.
Examine the photographs of the female shark's pelvic region by clicking the blue lettered links in the column to the right.
The cloacal opening located on the ventral surface between the pelvic fins. It receives the products of the intestine, the urinary and the genital ducts. The name cloaca, meaning sewer, seems quite appropriate.
Examine the photographs of the skinned shark by clicking the blue lettered links in the column to the right.
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 of the body that propels the shark foward.