MARE 394 – Sharks, Skates, & Rays
Anatomy Guide
Digestive System
Esophagus – The esophagus is the thick muscular tube extending from the top of the
cavity connecting the oral cavity and pharynx with the stomach. . Lined with esophageal
papillae, the esophagus leads into the "J"-shaped stomach.
Stomach –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. 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.
Intestine - The duodenum is a short "U"-shaped portion of the small intestine that
connects the stomach to the intestine. The bile duct from the gall bladder enters the
duodenum. 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; this section is
called the 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 primary function of the duodenum is digestion; function of
the spiral valve is absorption of nutrients. The colon is the narrowed continuation of the
valvular intestine. It is located at the posterior end of the body cavity.
Pancreas - located on the duodenum and the lower stomach. It also produces digestive
enzymes that pass into the small intestine. These enzymes help in the further breakdown
of the carbohydrates, protein, and fat. The secretions of the pancreas enter the duodenum
by way of the pancreatic duct.
Spleen - functions in the creation, storage, and destruction of redundant red blood cells.
Also aids in immune response by creating B & T lymphocytes; part the Lymphatic
system, the spleen is closely associated with the digestive organs in all vertebrates.
Liver - the largest organ lying 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 much shorter lobe is located medially and contains the green gall bladder along
its right edge. The liver is rich in oil which stores energy for the shark. The oil's low
specific gravity is also responsible for giving the shark a limited amount of buoyancy. It
plays a major role in metabolism and has a number of functions in the body, including
glycogen storage, decomposition of red blood cells, plasma protein synthesis, and
detoxification. It produces bile, an alkaline compound which aids in digestion, via the
emulsification of lipids.
Rectal gland - 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.
Cloaca - 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.
Urogential System
Kidney – role is to maintain the homeostatic balance of bodily fluids by filtering and
secreting metabolites (such as urea) and minerals from the blood and excreting them,
along with water, as urine.
♂ - Male Urogenital
Testis (2) – function in producing sperm (spermatozoa) and producing male sex
hormones that of which testosterone is the best-known
Efferent ductules (or efferent ductules or ductuli efferentes) - connect the testis with the
initial section of the epididymis
Epididymis – sperm maturation and storage
Vas deferens – contract to propel sperm during ejaculation
Sperm sac - paired sperm sacs at the posterior ends of the seminal vesicles receive the
seminal secretions. They join to form the urogenital sinuses which exit through the
urogenital papilla.
Urogential papilla – the fleshy conical end of the urogenital sinuses which extends from
the cloaca.
Cloaca – common duct which receives genital and urinary products as well as the rectal
wastes.
Claspers - modified extensions of the medial portions of the pelvic fins. They are inserted
into the female's cloaca during copulation. 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.
♀ - Female - Urogenital
Ovary (2) - 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 (ostium) are moved into the oviducts. Function in egg and hormone
production.
Ostium - the opening in the infundibulum of uterine tube into the abdominal cavity. In
ovulation, the oocyte enters the Fallopian tube through this opening.
Oviduct (2) – (Fallopian tube) elongated tube-like structures lying dorsolaterally the
length of the body cavity, along the sides of the kidneys. In mature specimens they are
more prominent. The distal half of the oviduct is enlarged to form the uterus. The
Fallopian tubes are not directly attached to the ovaries, but open into the peritoneal cavity
(essentially the inside of the abdomen); they thus form a direct communication between
the peritoneal cavity and the outside via the vagina. When an ovum is developing in an
ovary, it is encapsulated in a sac known as an ovarian follicle. On maturity of the ovum,
the follicle and the ovary's wall rupture, allowing the ovum to escape and enter the
Fallopian tube. There it travels toward the uterus, pushed along by movements of cilia on
the inner lining of the tubes. This trip takes hours or days. If the ovum is fertilized while
in the Fallopian tube, then it normally implants in the endometrium when it reaches the
uterus, which signals the beginning of pregnancy. Occasionally the embryo implants into
the Fallopian tube instead of the uterus, creating an ectopic pregnancy, commonly known
as a "tubal pregnancy".
Shell gland - anterior end of the oviduct. The eggs are fertilized and receive a light shelllike covering as they pass through the shell gland.
Uterus - 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 the young are ready to be born.
Cloaca - serves for the elimination of urinary and fecal wastes as well as an aperture
through which the young "pups" are born.
Fertilization in the dogfish shark is internal, usually taking place within the shell gland of
the oviduct. The fertilized eggs continue to move posteriorly to the uterus. As they grow
the pups are attached to the egg, now known as the yolk sac, by means of a stalk. During
its period of gestation, the yolk is slowly absorbed by the shark "pup."
Circulatory System
Fish have a two-chambered heart when compare with other vertebrates (1 atria & 1
ventricle).
Ventricle - the thick muscular walled cavity that pumps blood through the conus
arteriosus to the gills and the body.
Conus arteriosis contains a series of semilunar valves that direct the blood flow.
Atrium is thin-walled with two lateral bulging lobes. It pumps blood to the dorsal
ventricle.
Sinus venosus – region where blood enters the heart which drains into the atrium.
The posterior cardinal sinuses receive blood from the posterior parts of the body and
drain through the common cardinal veins into the sinus venosus.
The anterior end of the conus arteriosus continues foward as the ventral aorta. It gives off
five pairs of afferent branchial arteries which carry deoxygenated blood from the heart to
the gills.
Afferent branchial arteries - pass laterally from the medial ventral aorta carrying
deoxygenated blood to the gills. These afferent vessels enter the interbranchial bars and
serve the holobranchs of the gill arches.
Efferent branchial arteries - serve to return oxygenated blood from the gills. This blood
is then distri bused to all parts of the body. Four pairs of arteries may be seen arising
from the gills and uniting in the midline to form the median dorsal aorta.
The efferent branchial arteries give off many branches. These carry oxygenated blood to
the more anterior parts of the shark's body.
The four pairs of efferent branchial arteries join at the dorsal midline to form the large
dorsal aorta.
Dorsal aorta - passes posteriorly bringing oxygenated blood from the gills to virtually
every part of the shark's body.
Nervous System
The nervous system functions in communication between the various parts of an
organism and between the organism and its external environment. It 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.
Forebrain
Olfactory bulbs - paired extensions of the anterior portion of the brain. They are rounded
masses which make contact anteriorly with the spherical olfactory sacs, the organs of
smell.
Cerebrum (Cerebral hemispheres) - are the rounded lobes of the anterior brain. The
neural networks of the cerebrum facilitate complex behaviors such as social interactions,
learning, and working memory.
Olfactory lobes - anterior portions of thee cerebrum; processes “smell” information from
the olfactory bulbs
Optic lobes are a pair of prominent bulged structures that coordinate “sight” information..
Cerebellum is an oval-shaped dorsal portion that partly overlaps the optic lobes; plays an
important role in the integration of sensory perception, coordination and motor control.
Medulla oblongata is the elongated posterior region of the brain that is continuous
posteriorly with the spinal cord. It deals with autonomic functions, such as breathing and
blood pressure. The cardiac center is the part of the medulla oblongata responsible for
controlling the heart rate.
The cranial nerves originate in the brain and exit at the chondrocranium. These nerves
may be sensory, carrying impulses to the brain; they may be motor, carrying impulses
from the brain to muscles and glands; or they may be mixed nerves, carrying both
sensory and motor fibers.
The cranial nerves of all vertebrates have similar names and similar functions. Fish are
usually described as having ten pairs of cranial nerves including:
(I) Olfactory is a sensory nerve originating in the olfactory epithelium of the olfactory sac
and terminating in the olfactory bulb of the cerebral hemisphere.lt is concerned with the
sense of smell.
(II) Optic nerve is also a sensory nerve. It originates in the retina of the eye, exits the
back of the orbit, passes medially and posteriorly to the optic chiasma and enters the optic
lobes.
(III) Oculomotor nerve innervates superior rectus, medial rectus, inferior rectus, and
inferior oblique, which collectively perform most eye movements
(IV) Trochlear nerve innervates the superior oblique muscle, which depresses, pulls
laterally, and intorts the eyeball; Located in superior orbital fissure
(V) Trigeminal nerve arises from the anterior end of the medulla. It is a mixed motor and
sensory nerve which has four branches that inervate the face, eyes, mouth and jaws. The
superficial opthalmic nerve is one of the four branches. It has a general sensory function
for the skin of the rostrum.
(VI) Abducens nerve innervates the lateral rectus, which abducts the eye
(VII) Facial nerve provides motor innervation to the muscles of facial expression and
stapedius, receives the special sense of taste from the anterior 2/3 of the tongue, and
provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal
gland.
(VIII) Vestibulocochlear nerve Innervates the lateral rectus, which abducts the eye
(IX) Glossopharyngeal nerve receives taste from the posterior 1/3 of the tongue, provides
secretomotor innervation to the parotid gland, and provides motor innervation to the
stylopharyngeus (essential for tactile, pain, and thermal sensationis the longest of the
cranial nerves.
(X) The vagus nerve is the longest of the cranial nerves. It is a mixed motor and sensory
nerve that arises at the posterior end of the medulla. It innervates the gills, throat,
esophagus, stomach, intestine and body wall.
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.
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.
Sclera is the tough white fibrous outer coat of the eye. At places it is made even more
firm by cartilage embedded in the sclera.
Iris is the pigmented anterior extension of the choroid layer. In its center is the pupil. The
iris regulates the size of the pupil.
Retina is the multi-layered sensory gray-white colored membrane. The rods and cones
which receive light stimuli are located here. The optic nerve leaving the eye is a
continuation of the light receptor cells in this membrane.