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Dogfish Dissection
Do not write on this!
Objective: The Spiny
Dogfish is a small,
cartilaginous fish that has
long been a popular
specimen for study in the field of comparative anatomy. Its popularity is due to its
large numbers and consequent ease of capture in the sea, convenient storage, and
representative anatomy of primitive jawed fish.
The purpose of this lab is to compare the anatomy of the spiny dogfish with the
human through a dissection. This is an extremely important lab grade. It is
approximately 5 percent of your semester grade. You need to do a good job on this
to maintain your grade in this class. Chose your partners wisely (you will need to
work in groups of 4 or 5); if you have an unexcused absent during this time period
it will count against you! The due date will be posted on line. I will NOT
ACCEPT ANY LATE WORK on this assignment, even with a late pass.
1) You will work in groups of four or five. This is due to the extreme expense
of the specimens. You may discuss your definitions with your partners, but
you may NOT COPY the definitions word for word. IF YOU COPY
You will need to type up your definitions. You may want to split up the
sections to make sure everyone is working and the lab is completed. I will
be grading you on participation. Your partners will also decide whether you
deserve full credit or not.
2) Now it is time to receive a stinky, oily sharky to play with. You will also
receive a garbage bag to store your shark. Do NOT throw this away. You
will need this bag for the entire dissection. I do NOT have any extras.
3) The first thing we will do is to compare the anatomical structure of the shark
and the human. Place your specimen on a dissecting tray and examine its
FUNCTION OF THE STRUCTURES). Note that its shape is streamlined,
enabling it to glide easily through the water with the least possible
resistance. The body is divided into three anatomical regions: the head,
which extends from the tip of the snout to the pectoral fins; the trunk, which
continues to the origin of the tail; and the tail, which is at the posterior end.
4) Draw, label and tell me the function of the following features: Caudal
Dorsal Fin, Cranial Dorsal Fin, Caudal Fin, Dorsal Spine, Endolymphatic
Pore, External Gill Slits, Eye, Eye Lid, Interbranchial Septum, Lateral Line
System, Mouth, Naris, Pectoral Fin, Pelvic Fin, Spiracle, and Spiracular
Answer the questions on sharks on your observation sheet. Make sure
these are in your own words and don’t copy from your partner.
5) You will be taking measurements of your shark before you cut the shark.
What parts you need to measure are located in the table below; most of you will
not have a dorsal spin. When I ask you to measure the caudal and dorsal lobe,
that is referring to layers of the caudal fin. Make sure all measurements are in
centimeters. The actual measurements are recorded on your observation sheet.
Reproductive structure
5. Next you will determine the sex of your dogfish (Record this on your
observation sheet). Do this by flipping your shark so its ventral side is facing
up, and now look between the pelvic fins. Use the diagrams in the shark packet
“External Anatomy” to help identify the sex of your shark. You only draw,
label and define the sex of shark you are dissecting. You will need to draw,
label and give me the function of the following parts:
Male: anus, clasper, cloacal aperture, pelvic fin, and urogenital papilla.
Female: anus, cloacal aperture, pelvic fin, and urinary papilla.
Muscular structure (CUT #1)
6. Follow the procedure below to skin your shark. You will draw the muscles
that you see. You will not need to tell me the function of each muscle, but you
will need to label them. ONLY SKIN YOUR SHARK ON ONE SIDE!!!! To
view them, remove a strip of skin from one side of the dogfish. You will begin
on the dorsal midline cutting caudally from the Caudal Dorsal fin toward the
Caudal Fin. This may be done by making a shallow incision. You will gently
peel away the skin; be careful to not rip off the muscle (the skin is only 1/16 of
an inch thick). Remove the skin all the way to the ventral midline of the shark.
You will have removed all of the skin from the top of the shark towards the
bottom and all the way back towards the tail.
7. In order to expose the coelom (internal body cavity), the body wall must first
be dissected. To do this, follow the procedure below:
- Place your specimen on a tray on its back to expose the ventral side.
Using sharp scissors make a shallow incision through the skin layer from
a point immediately cranial to the cloaca to the pectoral girdle slightly to
the left of the midventral line (use Fig. 4.1 in your “Internal Anatomy”
handout as a reference). It is important to avoid cutting along the midline
near the pectoral girdle in order to prevent damage to underlying
structures. Now cut through the muscle layer by making a deeper incision
along the same path as the first incision through the skin.
- Carefully extend the incision made above from the coracoid bar of the
pectoral girdle to the level of the second gill slit. Cut through the body
wall, but do not cut deeply.
- Make a transverse incision through the body wall about midway between
the pectoral girdle and the pelvic girdle. Extend the cut on both sides to
the lateral line.
- This WILL BE MESSY because of the oils found in the shark’s liver.
Do not remove the flaps of skin so you can store your shark.
8. Draw, label and define the following: Cloaca, Duodenum, Gall bladder, Heart,
Liver, Pancreas, Pericardial Cavity, Spleen, Stomach, Transverse Septum, Uterus,
and Valvular Intestine. If any of these terms are repeated you will not need to
define them twice.
ORAL CAVITY: (CUT #3) The mouth or oral cavity is the space between the
external ridge of the teeth and the internal opening of the spiracles. To view the
oral cavity, follow the procedures below:
-Begin the incision by cutting through the left corner of the mouth. BE
9. Continue this cut through the Meckel’s cartilage, cartilages of the branchial
arches and the hyoid arch. Look at figures 5.1(In the Digestive and Respiratory
Handout) for a reference. Draw what you see on the observation page. You will
need to label the following features and give their functions: tongue, teeth,
spiracle, esophagus, and the pharynx.
10. Examine the digestive tract of the shark. Most of the structures you have
already seen, but I would like you to draw and label only the digestive tract.
Explain to me how the digestive system of a shark works. You may cut into the
stomach and intestines to see if the shark has eaten anything.
11. You will now view the internal structure of the heart. The heart must be
removed in order for it to be viewed. Cut the attachments of the sinus venosus to
the transverse to the transverse septum. Now cut through the ventral aorta near its
union of the fourth and fifth artery. Once the heart is removed you will draw a
picture of the interior of the heart. You will need to label all the parts, but you
only need to tell me the function of the following: atrium, ventricle,
atrioventricular valve and the conus arteriosus.
12. Now you will look at the brain from the dorsal aspect. Remove the skin and
other tissues from the dorsal surface of the head and around the eye. Carefully cut
away the dorsal portion of the chondrocranium to expose the cranial cavity. You
do not need bone cutters, scissors and scalpel should be fine. Continue to expose
the brain by removing the supraorbital crest. Draw and label what you see. Give
me the function of the following parts of the brain: olfactory tract, telencephalon,
prosencephalon, mesenscephalon, rhombencephalon, myelecencephaln,
metencephaln, tectum, and diencephalon.
13. Finish your dissection by examining the ear of the shark. First locate the two
endolymphatic ducts near the dorsal midline between the spiracles. Scrape the skin
away from this region. Next slice the cartilage away in the thing sections until you
can see the inner ear through its transparency. Label and give me the function of
the following: utriculus, anterior semicircular duct, crista, ampulla, external
spiracular pore, sacculus, horizontal semicircular duct, and posterior semicircular