Download File - Bowie Aquatic Science

LAB: Squid Dissection
Mollusks are soft-bodied animals and include nails, clams, octopus,
squid, and slugs. They are bilaterally symmetrical and have well-developed digestive,
circulatory, excretory, and respiratory systems. Squid are characterized by a large prominent
head with conspicuous eyes and a mouth surrounded by ten tentacles. The class Cephalopoda,
which includes the squid and the octopus, is considered to be the most complex and highly
developed group of mollusks.
OBJECTIVES
• Dissect and identify the organs and major organ systems of the squid.
• Describe the major features of the squid phylum.
• Determine the function of various squid features.
PROCEDURE
Part A. Body Organization
1. Put on the laboratory apron. Place the squid in the dissecting pan. Note that there is no
external shell and that the major part of the body is enclosed by the soft, muscular mantle.
There are ten conspicuous arms or tentacles, derived from the mollusk foot.
2. Identify and label the dorsal, ventral, posterior and anterior surfaces on your lab
worksheet (#1) using the following descriptions. The tentacles and arms of the squid are
located on the ventral surface of its body. The long, pointed body tube with the two fins
tapers dorsally, so the “tail” is actually the dorsal end of the body. The siphon, or funnel, is
located on the posterior surface. The fins are attached on the anterior surface. While
snakes snails, and cats move along an anterior-posterior axis, a squid moves along a dorsalventral axis.
3. Lay the organism in the dissection tray with the tentacles pointing towards you and the
mantle tapering away from you. On the figure you labeled add the labels for tentacles, eye,
mantle, fin, and siphon (#2). Turn the animal so that the siphon faces you. The eyes should
be on the right and left sides of the body.
4. Spread the tentacles and arms apart to reveal the beak and mouth. Count the tentacles and
arms while noticing the distribution of the suckers on the arms and tentacles. Answer #3 on
your worksheet.
5. Examine the beak and, if possible, work the parts together to discover how the can tear into
prey. BE VERY CAREFUL! The beak can be pulled out with minimal force and we are
not ready to do that. Answer #4 and #5 on your worksheet.
6. See Figure 2: Slit open the mantle cavity by inserting the tip of the scissors under the
mantle at the siphon and cutting to the apex (apex means top). Cut with care so that you do
not disturb the internal organs.
4. Pin down the mantle to the pan, slanting the pins at an angle away from the specimen as
shown in Figure 2.
Figure 2.
Siphon
Collar
Part B. Mantle Cavity and Respiratory System
1. Examine the mantle cavity. The walls of
the mantle cavity are very muscular. This
cavity is involved in propelling a squid
through the water. In the living squid, the
mantle cavity expands by muscular action
and fills with water. The collar locks
tightly against the head, leaving the
siphon as the only exit for the water. The
mantle muscle then contracts and water is
squeezed out through the siphon. This
method of movement is referred to as jet
propulsion.
2. Examine the siphon. The siphon is well
equipped with muscles and can be pointed
for directional jet propulsion. Note that
the tip of the siphon has a muscular valve.
3. Find the two gills shown in Figure 3.
These structures are oriented so that
incoming water passes over them.
4. Locate and remove the pen, the vestigial
internal shell. Grasp the tip of the pen and
tug GENTLY. Label according to #6 on
your worksheet.
Part C. Feeding and Digestive Systems
1. Examine under the hand lens the structure and organization of the suckers. The suckers,
which are located on the tentacles, are used to hold onto prey.
2. Remove the siphon and, with the scissors,
make an incision into the head. Expose the
beak as shown in Figure 4. Pry open the
beak and observe the tongue-like radula.
Trace the esophagus, which is surrounded
by the liver, to the thick-walled stomach.
The stomach emerges to form the caecum.
Note the pancreas. The intestine runs from
the stomach and terminates in the rectum.
After tracing this on your organism, use the
bold terms above to fill out #7 on your
worksheet. An ink sac arises from the
intestine near the anus, which is located near
the siphon. It is used for defense.
Part D. Circulatory, Excretory, Nervous, and Reproductive Systems
1. Locate the systemic heart as shown in
Figure 5. This is a difficult structure to
find because it is transparent.
2. Examine the nephridium, a kidneylike
excretory organ that removes liquid waste
products from the blood.
3. Locate the white mass of the cranium
above and between the eyes. This
structure contains the squid's brain.
4. Locate the reproductive organs as shown
in Figure 6. Determine the sex of your
squid, but be sure to examine squid of
both sexes. The male has testes that lie
beneath the caecum. The female has two
large nidamental glands that secrete a
protective covering over the eggs. Eggs
might or might not be present.
5. Remove the eye and CAREFULLY cut it
in half. Examine the transparent lens and
the shiny black retina at the back of the
eye. As you move things around some of
the pigmented particles of the retina may be
released. (Answer #8 on your worksheet).
Try to determine where the lens is in
relation to the cornea, iris and retina and do
your best to label the parts of the eye (#9 on
your worksheet). See if you can pull out the
lens and place it on a paper towel. Is the
lens soft or hard?