Shark Anatomy

lateral line
pale line that extends noticeably from the pectoral fin past the pelvic fin, this line is actually a group of small pores which open into the underlying lateral line canal, a sensory organ that detects water movements

dorsal fins
The spiny dogfish has a double dorsal fin. The anterior dorsal fin is larger than the posterior dorsal fin.

just cranial to each dorsal fin is a spine that is used defensively by the shark, each spine has a poison gland associated with it

caudal fin
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.

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.

gill slits
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.

pectoral fins
The paired pectoral fins act like an airplane’s wings to provide the lift needed to keep the shark from sinking

pelvic fins
The paired pelvic fins are located on either side of the cloacal aperture. They are different in males and females

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.

Ampullae of Lorenzini
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.

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.

cloacal opening
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.

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.

A smooth, shiny membrane called peritoneum can be seen lining the inside of the body wall.

The visceral organs are suspended dorsally by a double membrane of peritoneum know as mesentery.

The liver is the largest organ Iying within the body cavity. Its two main lobes, the right and left lobes, extend from the pectoral girdle posteriorly most of the length of the cavity. A third lobe

gall bladder
A third lobe much shorter lobe is located medially and contains the green gall bladder along its right edge.

The esophagus is the thick muscular tube extending from the top of the cavity connecting the oral cavity and pharynx with the stomach.

stomach-cardiac/pyloric (J-end)
The esophagus leads into the “J”-shaped stomach. The upper portion, the cardiac region, continues as the main body, and ends at the duodenal end.

The mucosa is the inner lining of the stomach.

The rugae are longitudinal folds that help in the churning and mixing the food with digestive juices.

pyloric sphincter
A circular muscular valve, the pyloric sphincter, is located at the far end or pyloric end of the stomach. It regulates the passage of partially digested food into the intestines.

The duodenum is a short “U”-shaped portion of the small intestine that connects the stomach to the intestine.

bile duct
The bile duct from the gall bladder enters the duodenum.

The pancreas is located on the duodenum and the lower stomach. The secretions of the pancreas enter the duodenum by way of the pancreatic duct.

The dark, triangular-shaped spleen is located near the posterior end of the stomach. Although a part the Iymphatic system, the spleen is closely associated with the digestive organs in all vertebrates.

valvular/spiral intestine
The valvular intestine is the second, and much larger, portion of the small intestine. It follows the duodenum and its outer surface is marked by rings.

spiral valve
The spiral valve is the screw-like, symmetrical shape within the valvular intestine. It adds surface area for digestion and absorption to an otherwise relatively short intestine.

The colon is the narrowed continuation of the valvular intestine. It is located at the posterior end of the body cavity.

rectal gland
The rectal gland is a slender, blind-ended, finger-like structure that leads into the colon by means of a duct. It has been shown to excrete salt (NaCI) in concentrations higher than that of the shark’s body fluids or sea water. It is thus an organ of osmoregulation, regulating the shark’s salt balance.

The cloaca is the last portion of the alimentary canal. It collects the products of the colon as well as the urogenital ducts. It is a catch-all basin leading to the outside by means of the cloacal opening.

The gills are the respiratory organs of the shark. They are composed of gill lamellae, blood vessels, and supporting cartilaginous structures are are located in a series of pharyngeal pouches.

pharyngeal pouches
pouches for gills, blood vessels, and supporting catilaginous structures

The tongue of the shark is practically immovable and without muscles. It is supported anteriorly and posteriorly by cartilage.

The pharynx is the portion of the alimentary canal posterior to the hyoid arch between the gills. Posteriorly it narrows to form the esophagus.

spiracle (internal view)
The spiracles are openings in the anterior roof of the pharynx. The shark can bring water into its pharynx to the gills by way of the spiracle and mouth.

gill slits
five internal gill slits lead into cavities called gill pouches, which lead to the outside by external gill slits.

gill arch
The gill slits are supported by cartilaginous gill arches

gill rakers
gill slits are guarded by small cartilaginous papillae-like gill rakers which act as strainers to prevent food particles from leaving the pharynx through the gill slits.

gill lamellae (gill filaments)
The gills are provided with a rich blood supply. Arteries run directly from the nearby heart to the gills bringing deoxygenated blood into the gill lamellae. Oxygen diffuses from the ventilating water current flowing over the gills into the blood.

pericardial cavity
The pericardial cavity is the upper portion of the body cavity. It is much smaller than the lower cavity, which contains the digestive organs.
The pericardial cavity is located anterior to the transverse septum and contains the heart and the major blood vessels leading to and from the heart.

sinus venosus



conus arteriosus

ventral aorta


dorsal aorta

to the body

The kidneys are flattened, ribbon-like, darkly colored structures Iying dorsally on either side of the midline, along the entire length of the body cavity. A tough white glistening strip of connective tissue is found between the kidneys in the midline. The kidneys of the male are essentially the same as those of the female. The posterior portion is involved in the manufacture and transport of urine. The main difference lies in the anterior portion of the kidney, which in females is degenerate and functionless, but in males is an active part of the reproductive system.

Paired testes lie near the anterior end of the body cavity, dorsal to the liver, adjacent to the anterior ends of the kidneys.The sperm pass from the testes to the kidneys within narrow tubules called efferent ductules.

ductus deferens (male vs. female)
After passing through the anterior end of the kidney the sperm enter the ductus deferens and pass posteriorly toward the cloaca. In mature male specimens the ductus deferens may be seen on the ventral surface of the kidneys as a pair of highly coiled tubules. Note: While in the female this duct carries urine, in the male it transports spermatozoa and seminal fluid. The posterior portion of the ductus deferens widens and straightens to form the paired seminal vesicles.

The cloaca receives the genital and urinary products as well as the rectal wastes.

The claspers are modified extensions of the medial portions of the pelvic fins. They are inserted into the female’s cloaca during copulation. The finger-like claspers each have a dorsal groove, the clasper tube that carries the seminal fluid from the cloaca of the male to the cloaca of the female during mating.

The ovaries are two cream-colored elongated organs in the anterior part of the body cavity dorsal to the liver on either side of the mid-dorsal line. The shape of the ovaries will vary depending upon the maturity of the specimen. In immature females they will be undifferentiated and glandular in appearance. In mature specimens you may find two to three large eggs, about three centimeters in diameter, in each ovary. When these break the surface of the ovary, upon ovulation, they enter the body cavity and by means of peritoneal cilia are moved into the oviducts.

reproductive organs; male-claspers, female-ovaries

shell gland
The shell gland is the anterior end of the oviduct. The eggs are fertilized and receive a light shell-like covering as they pass through the shell gland.

The posterior half of the oviduct becomes enlarged and is known as the uterus. The fertilized eggs develop into embryos in the uterus. Upon completing their period of gestation (close to two years) the young are ready to be born.

producing eggs that are hatched within the body, so that the young are born alive but without placental attachment

bringing forth living young rather than eggs

porducing eggs that mature and hatch after being expelled from the body

olfactory bulbs/sacs
The olfactory bulbs are a paired anterior extension of the brain leading into the posterior end of the olfactory sacs. Their fibers continue into the olfactory tract and the olfactory lobe of the cerebral hemisphere. The olfactory sacs are spherical structures that contain a series of radial folds called olfactory lamellae. Their surfaces are covered with olfactory epithelium. Sea water taken into the nares is passed over these sensory areas. Here the odors stimulate the cilia-like endings of neuro-sensory cells.

optic lobes
The optic lobes are a pair of prominent bulged structure.

medulla oblongata
The medulla oblongata is the elongated posterior region of the brain that is continuous posteriorly with the spinal cord.

Anterior Dorsal Fin 1st fin on the ‘top’ of the shark, bigger than the 2nd used for balance. Labeled E in the picture Posterior Dorsal Fin 2nd fin on the ‘top’ of the shark, smaller than the 1st fin, used …

Placoid scale a toothlike spine found on shark skin lateral line system A pale line that extends noticeably from the pectoral fin past the pelvic fin. This line is actually a group of small pores which open into the underlying …

How many species of fish are there? 20-30,000 What is the smallest and biggest fish species? Smallest = Philippine Island goby fish gill slits What are the small teeth-like structures found on the branchial arch called? Gill rakers They filter …

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