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General Zoology
BIOL 2154
Chordate Lab #2
Part 1. Shark Dissection
1. Sharks are members of Phylum Chordata and Class Chondrichthyes. What kind of skeleton do they have?
______________________________________
2. “The skeleton may be partially calcified to some extent with calcium phosphates and carbonates, particularly in
the vertebral column. The calcified cartilage is not a true bone. The cartilage of a shark's skeleton may be
important in future cancer research. Shark cartilage contains an active ingredient that has been known to inhibit
tumor growth. In addition, sharks rarely develop cancer. A shark's cranium is a single compact cartilaginous
block which encloses the brain, olfactory, and auditory capsules. Jaws are loosely attached to it. Without hard
bones, red blood cells are produced in the kidneys and a special organ called an epigonal. White blood cells are
created in the spleen and spiral valve within the intestine.” 1
3. Identify the external features as listed below. What is the function of the lateral line?
___________________________________________________________________
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4.
Note the external features that determine whether or not your shark is male or female. Which gender do you
have? __________________________________ Look at a shark of the opposite gender.
5. “Claspers are modified inner edges of the pelvic fins of male sharks and rays. During copulation, the erectile
claspers are bent forward. The male inserts one clasper at a time into the female. In some species, claspers
contain cartilaginous hooks and spurs that "clasp" into the walls of the female oviduct, anchoring the clasper.
Muscles force seminal fluid down a groove in the clasper and into the female oviduct.” 1 What type of
fertilization do sharks have? _______________________________________________
6.
How many gill slits does your shark have? ______________ How many are characteristic of Class
Chondrichthyes? _____________________
7. What is the function of the spiracle? (See below on information about the gills)
______________________________________________________________________________________
8. “The esophagus is short and wide, barely discernible from the stomach. A U-shaped stomach leads to a spiral
valve in many species. A spiral valve is the lower portion of the digestive tract. It is internally twisted or coiled
to increase the surface area, which increases nutrient absorption. After the spiral valve, the digestive tract leads
to the rectum and to the cloaca. The cloaca is a common opening for the urinary, digestive, and reproductive
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systems. If a shark eats something terribly upsetting, some species can force their stomach out through their
mouth and into the water to empty it out. Some sharks have highly specialized stomachs. If threatened, the
balloon shark (Cephaloscyllium sufflans) can rapidly inflate its stomach with air or water just like pufferfish and
porcupinefish.” 1
9. “A shark's liver is made of two large lobes that concentrate and store oils and fatty acids. The liver functions in
energy storage and buoyancy. A shark's liver is relatively large, making up 5% to 25% of its total body weight
and takes up to 90% of the space inside its body cavity.” 1
10. Be able to identify the stomach, liver, and valvular intestine (spiral valve).
11. “A shark's heart is a two-chambered S-shaped tube, small in proportion to body size. Blood flows from the heart
to the gills and then to body tissues. Fast-swimming sharks, such as great whites and makos, have a body
temperature that can be quite a bit higher than the surrounding water (up to 8°C or 14.4°F higher). The heat is
due to the modified circulatory system associated with the red muscle. As red muscle functions, it generates
heat. Muscle-generated heat warms the blood circulating through the red muscle, which then travels back to
the heart through veins. Thus, blood returning to the heart from the muscle is warmer than blood traveling from
the heart to the muscle. Due to the nearness of arteries and veins, heat passes from warmer veins to cooler
arteries within the shark's body, rather than dissipating to the cooler environment. This modified circulatory
system retains heat in the red muscles. Sharks have a low blood pressure. The walls of the pericardium (the
membranous sacs that enclose the heart) are rigid, creating a suction within the pericardium to maintain the
flow of blood. To circulate blood throughout their bodies, many sharks must swim continuously.” 1
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12. Identify the heart, atrium, and ventricle. Like other fish, the heart has only two chambers.
13. “Water enters the gill chambers through the mouth or spiracles and exits through the gill slits. In the past, it was
assumed that all sharks must swim to move water into their mouth and over their gills to respire. We now know
that sharks can respire by pumping water over their gills by opening and closing their mouths. However, many
sharks do have to swim continuously: due to their low blood pressure, muscular contractions are needed to
circulate their blood. Blood in the gill filaments absorbs oxygen from the incoming water. Gill rakers,
cartilaginous projections on the gill support structure, protect the delicate gill filaments from particles in the
water that might damage them. In species where they are present, spiracles provide oxygenated blood directly
to the eye and brain through a separate blood vessel which is reduced or absent in active, fast-swimming
sharks.” 1
14. Identify the gill arches, internal spiracle, and gill rakers. What function do the gill rakers serve?
____________________________________________________________________
15. Trace the flow of water through the shark, from the mouth and out the gill slits. List the structures the water
passes over or through. _______________________________________________________________
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16. Identify the testes, ovary, oviduct, and uterus (you will have to view another shark to see both sets of organs).
Do sharks have internal or external fertilization?
____________________________________________________
Images from:
http://jb004.k12.sd.us/MY%20WEBSITE%20INFO/BIOLOGY%202/ANIMAL%20KINGDOM/SHARK%20DISSECTION/SHARK
%20DISSECTION%20HOMEPAGE.htm
Additional information from:
1. http://www.seaworld.org/animal-info/info-books/sharks-&-rays/anatomy.htm
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Part 2. Perch Dissection
1. The perch is a member of Class Osteichthyes. What kind of skeleton does it have? ______________________
2. “Begin studying the external anatomy by first noting the general regions of the fish. The head extends from the
tip of the snout to the posterior tip of the operculum (gill cover). There is no neck and thus the head runs
directly into the trunk region which terminates at the anus located about two-thirds the length of the specimen
on the ventral surface. The tail begins behind the anus and terminates at the last vertebra. The distance
measured from the anterior tip to the last vertebra is called the standard length of the fish. The caudal fin,
which is not included in standard length, is inserted in the flesh behind the last vertebra and is included in the
total length. For taxonomic purposes, average standard lengths are usually given whereas the sports fisherman
wanting to boost his "bragging rights" will invariably use total length in describing the catch.” 1
3. “The trunk is divided into several areas for descriptive purposes. Most useful taxonomically are the positions of
the fins. Just posterior to the operculum are the pectoral fins, which are homologous to the shoulder and fore
limb-region of other vertebrates. The pelvic fins of the perch are only slightly posterior and ventral to the
pectorals. The entire, less pigmented ventral area is usually called the belly (not very scientific, but descriptive
none-the-less). The dorsal fin is composed of two distinct sections; the anterior most section has spiny rays and
posterior section has soft rays. This two-parted dorsal fin is a family characteristic of the Percidae. Just posterior
to the anus on the ventral surface of the animal is the anal fin with one sharp spiny ray and the remaining ones
soft. The number of rays in selected fins as well as their position on the body are often used as key
characteristics for genus and species separations. The homocercal caudal fin is the propulsion mechanism of the
animal. The thin lateral line located just dorsal to the mid-lateral area of the body extends from the operculum
to the caudal fin. It serves sensory functions for the animal.” 1
4. Examine the external anatomy, and identify the numbered structures below. What function does the operculum
serve? __________________________________________________________ Carefully remove the operculum
without removing the gills. How many layers of gills do you see? _________________________________
5. Does the perch have a lateral line? ______________________________
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6. “Study the head region of the fish. The area between the anterior orbit of the eye and front of the animal is
called the snout; it has a pair of openings, the nostrils located about half way back on the dorsal part of the
snout. The structures of the upper and lower jaws may be of taxonomic value. The forward, upper lip is called
the premaxilla and just posterior and slightly ventral to that is the maxilla. The lower jaw is called the mandible
and of course, as in other jawed vertebrates, is hinged. We have already mentioned the operculum or gill
covering, which is also divided into several parts. The eye is of special interest. Can you find a lid or membrane
covering it? _______________________________________ Why would such a membrane or lid not be
necessary in this animal? ___________________________________” 1
7. “With the scissors, cut a large section out of the body beginning at the posterior edge of the last gill and
extending dorsal to the pectoral fin, through the ribs and arching toward the anus. Cut around the anus and
then back forward between the pelvic fins to the posterior edge of the former operculum. Lift out this large
section of flesh and bone and view the underlying structures.” 1
8. First study the digestive tract and its associated organs. The false diaphragm separates the abdominal cavity
posterior from the anterior pericardial cavity that is located between and ventral to the gills. The first abdominal
organ that you should see is the brownish liver. Gently pull the liver back from the diaphragm and note two
veins that run from the liver through the diaphragm to the heart. The gall bladder is attached to the right lobe of
the liver. Behind the liver is the sac-like stomach. It is peculiar in that the esophagus from the pharynx and the
intestine from the stomach enter and leave respectively at the same end of the stomach. Such a close-ended
stomach is called a caecal stomach. The intestine loops back over itself once as it extends toward the anus. Close
to the stomach the intestine bears several blind pouches called pyloric caecae.
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9. “Cut the intestine about one centimeter forward of the anus and begin gently lifting it out of the body cavity.
The dorsal mesentery will likely inhibit this process and will therefore need to be cut away as the intestine is
lifted forward. Care should be taken to not remove any structures but the intestinal tract and the spleen. The
tract may be cut just forward of the stomach and completely cleared away.” 1
10. “The air (swim) bladder may be located as a tough membranous structure closely applied to the dorsal surface
of the body cavity. In life the air bladder would be inflated, but it will likely be collapsed in this specimen. Does
the air bladder have a homologue (similar organ) in other vertebrates? __________ _______________ What is
its function in this organism? ____________________________________ To help answer that question, the
darters (which are in the same family) lack an air bladder. These fish live in streams and lakes and are bottom
dwellers. The air bladder opens into the pharynx through tiny ducts that are not likely to be seen with the naked
eye. Dorsal to the air bladder is the dark colored kidney. It may be necessary for you to depress the air bladder
in order to observe the kidney.” 1
11. “Since the digestive tract has been removed and we have detached the air bladder, the remaining structures in
the body cavity are associated with reproduction. It is not possible for us to determine male from female until
we have opened the cavity. In the male a pair of long, milk white testes lie just dorsal to where the intestine had
been. They had to be moved out of the way in order to completely study the intestine. The two testes are united
along the posterior one third of their median surfaces and terminate as a single duct called the vas deferens.
Sperms are discharged through this duct to the outside via the urogenital opening, which is common with the
urinary discharge as well. In the female there is a single two-parted ovary lying in the middle of the abdominal
cavity. The ovary is within a membranous ovarial sac that is attached to the ventral body wall at its posterior
end, between the anal and urinary openings. Unlike most vertebrate organisms there is no permanent opening
for discharge of eggs, but instead when the eggs are mature, they are discharged through a temporary rupture
between the urinary opening and the anus. Since the eggs are discharged in water where currents may separate
them, a gelatinous matrix that is secreted by subsidiary ovarian tissue conveniently holds them together.” 1
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12. ”Now turn your attention to the area forward of the abdominal cavity, the pericardial cavity. Study as many
structures of circulation as you can on the specimen. The heart consists of two chambers, ventricle and auricle.
The two chambers may be differentiated by position and texture. The ventricle is ventral and anterior and is
thick walled while the auricle is thin walled posterior to the ventricle and slightly dorsal. Thus the heart is tilted
in the cavity with the auricle dorsal and the ventricle ventral. The auricle receives blood from the body through
veins which coverage just before the auricle into a single enlargement called the sinus venosus. On the ventricle
side of the heart it should be possible to observe the bulbous arteriosus. Extending forward from the bulbous is
the ventral aorta that branches four times - one for each pair of gills; these branches are termed afferent
arteries.” 1
13. “Study of the nervous system will be the final exercise of this lab. Cut into the bones of the cranium with sharp
scissors by inserting the tip of the scissors into the external nares and cutting posteriorly. Our intention here is
to expose the brain by cutting and chipping away bones of the cranial cavity. Once the cavity has been exposed,
carefully remove the fat cells that cover the brain. Careful work should expose the major divisions of the brain.
Beginning anteriorly the olfactory nerves are paired and pass posteriorly to the olfactory bulb. What is olfaction?
______________________________ Behind the olfactory bulb is an enlargement of the brain called the
telencephalon. What mammalian brain structure would it have as a homologue? _____________
___________________ Next is a bilobed brain structure that on its ventral side receives the impulses of sight;
these are called the optic lobes (tecta). Notice their size compared with the rest of the brain. It is obvious the
emphasis that the fish places on sight and smell from the amount of nervous tissue set aside for these sensory
functions. The cerebellum lies posterior to the optic lobes. Following this brain structure, the medulla oblongata
completes the brain and runs imperceptibly into the spinal cord. A darkened membrane called the choroids
plexus covers the dorsal surface of the medulla. This membrane partially conceals an opening into the brain
stem; the opening is the fourth ventricle. Although we will not try to locate them, the fish possesses ten cranial
nerves (some authorities say eleven) which receive sensory signals and pass them to the brain for clearing,
interpretation and action as is needed for the organism's well being (or perceived well being).” 1
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Key to images
1. Caudal fin
2. 2nd dorsal fin
3. 1st dorsal fin
4. Lateral line
5. Operculum
6. Pectoral fin
7. Pelvic fin
8. Anal fin
9. Nostril
10. Bulbus arteriosus
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Atrium
Ventricle
Gill filament
Liver
Stomach
Pyloric ceca
Swim bladder
Duodenum
Myomeres
Kidney
Images from:
http://www.cumberland.k12.il.us/Schools/CHS/Starwalt%20Projects/Perch%20Web%20Page/perch%20dissecti
on.htm
Additional information from:
1. http://www.msu.edu/course/lbs/158h/manual/Perchdissect.pdf (by Howard Hagerman)
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Part 3. Pigeon Dissection
1. Birds are members of Phylum Chordata and Class Aves. What structures are unique to birds? _____________
____________________________________________________________________________________
2. Identify the eternal features of the pigeon. Pay particular attention to the feathers. There are three types of
feathers: contour, down, and pinfeathers. The contour feathers cover most of the body, including the wings.
Down feathers are soft and fluffy. In juveniles they are the primary feathers. In adult birds they are found
between the contour feathers. Pinfeathers are small, almost hair-like structures found between the other
feathers. Pluck each from the specimen and look at them under a dissecting microscope. Describe how each
feather looks. _____________________________________________________________________________
_________________________________________________________________________________________
_________________________________________________________________________________________
3. Study the legs and feet. How does the skin here differ from the skin on the rest of the body? ___________
_______________________________________________________________________________________
4. Find the external ear opening. Are there any external structures like our ears? _______________________
What covers these openings? _________________________________
5.
Make an incision along the right side of the neck from the corner of the mouth to the breastbone (keel).
Identify the trachea, esophagus, and crop. The crop is used for temporary storage of food prior to digestion.
Remove a section of the trachea and look at it under a dissecting microscope. Do the cartilage rings completely
or partially encircle the trachea? ____________________ Why would this be an advantage during flight?
_______________________________________________________________________ Note the enlargement
at the base of the trachea, before it divides into the lungs. This is called the syrinx. What function do you think
it serves? _____________________________________________________
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6. Carefully cut into the abdomen at the base of the keel, and open the abdomen to the cloaca; try to avoid
damaging any of the internal organs. Carefully cut through the ribs along either side of the keel. Slowly remove
the keel by pulling it towards the head. As you do so, try to observe the delicate air sacs. It is impossible to
remove the keel without damaging them, but if you are careful you can see them. There are a total of nine air
sacs. These sacs have limited blood supply and do not function in gas exchange. They act as bellows or
reservoirs to help circulate air during both inspiration and expiration. Why would this be an advantage during
flight? _____________________________________________________________________________
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7. Notice that there is no diaphragm separating the thoracic from abdominal cavities. Birds breathe by expanding
their entire chest, not by contracting a diaphragm muscle like mammals. Observe the lungs along the dorsal
body wall. Remove one and view it under a dissecting microscope. Describe what you see. _____________
__________________________________________________________________________________
Birds have rigid lungs that do not expand and contract like other animals. Why would this be an advantage in
flight? _____________________________________________________________________________
8. Identify the heart and the large liver near it. Like mammals, a bird’s heart has four chambers. Trace the
esophagus to the digestive tract. The first large expansion is the proventriculus. This is the first part of the
bird’s stomach, and the location where digestive enzymes begin to mix with food. Just past this structure is the
gizzard, a round, thick-walled organ. The gizzard often contains small stones or grit. The heavy musculature is
used to break down hard food. A gizzard is also found in reptiles, earthworms, and some fish. The digestive
tract then continues into the small intestine. Why is such a structure necessary? _______________________
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9. Remove or push aside the digestive system and look at the dorsal side of the abdominal cavity. Many birds have
no external gender differences, so sexing must often be done by observing the gonads internally. The testes and
ova have a distinctly different appearance, and should be easy to differentiate based on the images below. Note
the oviduct leading from the ovary to the cloaca in the female. Be sure to observe both genders. Do birds have
internal or external fertilization? ___________________________________________________________
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10. With scissors, carefully cut away the skull, starting at the base of the head where the spinal cord attaches. The
large cerebral hemispheres are smooth, compared to the heavily wrinkled equivalents in many mammals
(including humans). What structure in humans is this equivalent to? ____________________________ What
structure in fish is this equivalent to? _________________________________________________ You should
also be able to observe the cerebellum just caudal to the cerebrum.
Animal
Phylum
Class
Type of
Skeleton
Respiratory
Organ
Fertilization
Heart
Chambers
Shark
Perch
Pigeon
Images from:
http://www.bio200.buffalo.edu/labs/tutor/Pigeon/Pigeon.html
http://jb004.k12.sd.us/MY%20WEBSITE%20INFO/BIOLOGY%202/ANIMAL%20KINGDOM/PIGEON%20DISSECTION/PIGEO
N%20DISSECTION%20HOMEPAGE.htm
http://www.mytoos.com/airsacs.html
http://people.eku.edu/ritchisong/RITCHISO/birdrespiration.html