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VERTEBRATE PRE-LAB:
SHARK DISSECTION
** NOTICE **
This pre-lab is a requirement. If you do not turn it in prior to the lab, you will not
be able to participate in the dissection. Completion of this pre-lab is a part of
your lab grade.
DISSECTION LAB SAFETY RULES
Read the following rules on dissection lab safety. Following these rules is a series
of questions you must answer.
 You must wear lab safety goggles at all times.
 Immediately inform your teacher of any illness or accident.
 Properly mount dissection specimens to dissecting tray. Do not dissect a
specimen while holding it.
 Handle scalpels, razor blades, and scissors with extreme care.
 Always cut away from your body and away from others.
 Never ingest specimen parts Properly dispose of dissected materials.
 Never remove specimens or specimen parts from the classroom. Until the
dissection is completed, all parts of the dissection must remain within the
dissecting pan.
 Store specimens as directed by your teacher.
 Clean up the work area and return all equipment to the proper place
when the dissection is completed.
 Wash your hands after each dissection.
BACKGROUND ON VERTEBRATES
The first vertebrates arose around 550 million years ago. Vertebrates are animals
with a backbone and an internal skeleton, a skull with a brain, and limbs. This
internal skeleton supports and protects the animal’s body, and it serves as a
place for muscles to attach. Unlike the exoskeleton of invertebrates, the internal
skeleton of vertebrates grows as the animal grows.
Another difference is that the
skeletons of invertebrates are made
entirely of non-living material. This is
not the case for vertebrates. Their
skeleton contains living cells, as well as
non-living material that is produced by
cells. The skeleton is made of
cartilage and/or bone. The outer
surface of their body is covered by
feathers, skin, scales, fur or hair, or
some combination of the above.
Vertebrates are a very diverse group, ranging from lampreys (a jawless, eel-like
fish) to humans. There are five classes of vertebrates. The easiest way to
determine what class a vertebrate belongs to is by looking at the body
covering. Here is a list of the vertebrate classes and their different body
coverings:
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Fish -- scales
Amphibians -- smooth or bumpy skin
Reptiles -- scales
Birds -- feathers
Mammals -- fur and hair
In Cambrian times, about 500 million years ago, the majority of the vertebrate
species were jawless fish. The decline of the jawless vertebrates and the
subsequent rise of the gnathostomes (fish with jaws) took place during the
Silurian Period, about 450 million years ago. This included sharks and their close
relatives, rays and skates.
BACKGROUND ON CARTILAGENOUS FISH
Cartilaginous fish such as sharks, skates, and rays are vertebrates whose internal
skeletons are made entirely of cartilage and contain no true bones. Cartilage
can be found in humans, in places like the nose, ears, ribs, bronchial tubes (air
passage to the lungs), and spine. Cartilaginous fish are also known as
Chondrichthyes and have one or two dorsal fins, a caudal fin, two pectoral fins,
and two pelvic fins that are supported by girdles of the internal skeleton.
Placoid scales, or dermal teeth, are characteristic of the
skin of both sharks and rays. The touch of shark's skin is
similar to the feel of sandpaper and was actually used as
this way for many years. The tiny teeth that protrude from
the skin vary in each species of shark.
The skin of rays is naked in places (without dermal teeth),
but on the back of or upper tail surface, the dermal teeth
have developed large, strong spines.
Stingray
The jaw teeth of both sharks and rays are in fact
modified dermal teeth, which are lost when they
become worn, and are replaced by rows of new
teeth from the space behind. In some species of
sharks, the jaw looks like an assembly line, with
new teeth filling spaces immediately.
Jaw teeth in rows
Both sharks and rays breathe through gills and have an opening called a
spiracle on both sides of the head behind the eye. The spiracle enables the
rays, which often bury in the sand, and seabed-resting sharks to take in water,
pump it through the gill chamber, and release it through the gill slits without
taking in large amounts of mud and sand. These fish usually take respiratory
water in through the mouth, extract the oxygen from the water in the gills, and
pass it out through the gill slits.
Cartilaginous fish do not have swim bladders, so a swimming motion must be
maintained continuously, even when sleeping, or they will sink to the bottom.
The caudal fin of the shark provides the propellant force in swimming, the dorsal
fin provides balance, and the pectoral fins are used for upward force and
depth rudders.
The pectoral fins in the male cartilaginous fish are also used for mating. The rear
part of the pectoral fin is modified into what are called claspers. These are used
to channel semen to the female during mating. All cartilaginous fish have
internal fertilization. Some species are egg-layers, and others hatch the eggs
within the female and give birth to live young. Still others have young that
develop in utero, similar to mammals, with a yolk sac supplying nutrients to the
embryo.
Cartilaginous fish are predatory, meaning that they feed on other animals, from
zooplankton to shellfish to whales. Cartilaginous fish themselves are sought after
by humans as a food source. Shark meat, once marketed under the
pseudonyms of "flake" and "steakfish" is now popular worldwide. Shark fins have
long been popular in Asia, presumably for their ability to keep a person from
getting cancer (which is completely untrue). Rays are considered delicacies in
Great Britain and France, and thornback rays and flapper skates are often sold
as sea trout.
Skate
Ecology Alert:
Sharks are fished for their meat, liver oil, cartilage and fins. The fins are
hacked off while the sharks are still alive, to be used in shark fin soup, an
ancient and prized delicacy in East Asia.
Over 100 million sharks are killed by humans each year.
WHICH SIDE IS WHICH?
The front of an animal is called the anterior end
The back of an animal is called the posterior end
The top of an animal is called the dorsal side
The bottom of an animal is called the ventral side
The arrow is pointing to the dorsal fin. It is located on the dorsal side of the shark.
DOGFISH SHARK ANATOMY
1. External nares: These are a pair of openings (nostrils) on each side of the
head. Water is taken into the smaller of the two openings, and expelled
through the larger opening. The water passes over a sensory membrane,
allowing the shark to detect chemicals in the water.
2. Spiracles: These are small openings above and behind the eyes. These
openings allow water to pass through the gills even when the shark’s
mouth is closed.
3. Mouth: Besides eating, the mouth is also used for the intake of water that
then passes over the gills.
4. Gill slits: Five vertical slits behind the mouth that allow water to exit after
passing over the gills.
5. Lateral line: A pale line that extends from the pectoral fins backward, past
the pelvic fins. This line is actually a group of very small pores that open
into a sensory organ that can detect movement in the water.
6. Cloaca: This both the exit to the digestive tract, and the opening for the
sex organs. The cloaca lies between the pelvic fins.
7. Claspers: Found on male sharks only. These are finger-like extensions of
the middle edge of each pelvic fin. The claspers aid in sperm transfer
during mating.
8. Fins: Refer to Figure 1 to familiarize yourself with each fin and its name.
9. Rostrum: The pointed snout at the anterior end of the shark.
10. Dorsal spine: Found just in front of each dorsal fin. These are used
defensively. If captured, the shark can arch its back to pierce its captor.
Glands at the base of the spines secrete a mild poison.
Questions:
1. What are the two biggest differences between invertebrates and
vertebrates?
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2. When did the first fish with jaws arise?
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3. What re the names of the four types of fins found on a shark?
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4. Why are the jaw teeth of cartilaginous fish sometimes referred to as an
“assembly line”?
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5. What is the difference between gills and spiracles?
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6. What are claspers?
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7. How many sharks are killed by humans each year?
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