Name __________________________________
Marine Biology--Mr. Nelson
PHYLUM MOLLUSCA--SQUID DISSECTION
Background:
Squid belong to the Phylum Mollusca in the Class Cephalopoda. This class also
contains the octopus, cuttlefish, and chambered nautilus. Cephalopods represent the
most advanced group of the phylum Mollusca. Cephalopods are characterized by
possessing the following advanced features:
1. Distinct head with large well-developed eyes and well developed brain.
2. Head projects into a crown or group of flexible, well muscled, arms.
3. Mouth with well developed jaws and a hard parrot-like beak for tearing off
food pieces.
4. All are active, quick, predators that are found only in marine habitats.
5. All cephalopods can swim rapidly by expelling water from their mantle
cavity.
Squids often evoke images of monsters of the deep, fighting off the giant sperm
whales, and although some can reach upwards of 15 meters (50 feet) in size, the
majority are shy, timid creatures which grow to about 30 cm long. They are among the
quickest members of the invertebrates. They can swim as fast as 20 km
per hour and leap as much as 3 m from the surface of the water. The giant squid is the
largest of all invertebrates. Most other mollusks have an external shell for protection
but the squid has a thick muscular mantle with an internal pen for support. They are
considered to be one of the most advanced of all of the invertebrates and are active
members of the nekton group. Squids are also a very important source of food for
many people around the world and their ink is used as a dye.
PROCEDURE:
Part A. External Parts of Squid
1. Place the squid in the dissecting pan. Stretch out the two tentacles and eight arms.
Arms: there are four pairs (eight) arms on the squid. Note the two rows of
stalked suckers which line the underside of each arm. Arms manipulate and
hold food while it is being eaten. In males, the fourth arm is used for the
transfer of spermatophores.
Tentacles: these are two (one pair) long appendages with suckers restricted to
pads on the distal ends. Tentacles are used to grasp prey and pull it to the
arms. Tentacles are a modification of the foot found in other mollusks.
2. Cut off the end part of a tentacle with the suckers attached. Put it in a petri dish so
that you can better examine the suckers with a dissecting microscope. Examine the end
section on one tentacle with the dissection scope. Note the small suction cup parts on
the tentacle. On the SQUID DISSECTION—Hard Copy Drawing, draw a
couple of these suckers below showing their attachment to the tentacle.
3. Note how each sucker has a set of teeth. These teeth grab the skin of prey or attach
on an object and by pulling with the arms a suction is created. This suction aids in
holding the object. The stalk connects the sucker to the tentacle or arm. It is flexible
and muscular which aids in securing prey. Label your drawing, from procedure
#2, with the two bold words from this section.
4. The body is the largest part of the animal but you cannot see all of it. Find the head.
It appears loosely attached to the body. The head has eyes on each side.
5. Behind the head the body is covered by the mantle. The two small flaps at the
tail end of the body are fins.
6. The opening to the body just behind the head is the collar. Locate the water jet on the
posterior where the collar opening and head meet. Squid swim by squirting water
away from their water jet. The direction the water jet faces allows the animal to swim
backward or forward.
7. Separate the arms and find the mouth. Notice the dark spot in the center of the
mouth. These are the jaws. I want you to remove the jaws in one piece. With the
forceps, carefully pull on the upper and remove it. Cut the muscles on the side of the
mouth, if necessary. Use the same procedure to remove the lower jaw. Place it with
the upper jaw and observe how they work together.
Why do people refer to the squid’s mouth as its beak?
8. Label the tentacle,
arm, body, mantle, head, eye, fin, collar,
water jet, and mouth on Figure 1.
FIGURE 1. Squid external anatomy
9. Besides being quick swimmers, squids also hide from their predators by controlling
the size of their pigment cells, called chromatophores located in the mantle. Their
coloration can change to blend in with the background in a matter of seconds by
controlling these cells. The squids are very streamlined in shape and they use their fin
along with the water forced out of the siphon for propulsion.
What is the reason for the squid's streamline structure?
10. They generally swim towards their posterior end, backwards, always seeing where
they have been, although their siphon is flexible and can be directed forwards or
backwards allowing for maximum maneuvering. Locate their eyes, on the side of their
head. These eyes are highly developed, somewhat similar to vertebrates, and this
allows them to see what is to the side of them.
Based on what you know about Turbidity, do you think the
squid can see as far through water as we can above? Why or
Why not?
11. Using
the arrow shapes in Word, add the correct arrow ends
to show the direction water will squirt out from each jet. Then,
use arrow shapes in Word to shade in the correct arrow ends to
show the direction the animal moves as water squirts from its
jet.
Part B. Internal Parts of the squid
1. Turn the squid over so that it is dorsal side up (the water jet is on the dorsal side).
Use forceps to hold the mantle up away from the internal organs. With scissors,
carefully cut through the mantle. CAUTION: Use care with scissors. Place the blade of
the scissors under the collar and cut toward the fins all the way to the end.
2. Pin the mantle open with some dissection pins. Use care in finding the internal
organs as you will have to point them out to Mr. Nelson. If you hack them up, I can’t
give you credit for that part. Gently use dull probes!
3. Use your diagrams to identify, without damaging, the parts in the procedure below.
4. Find the black ink sac. It may have some dark ink in it and it runs along the
intestine. Usually we see the ink has become granular as the squid have sat in
preservative.
5. Locate the stomach, the white, muscular sac-like organ attached to the esophagus at
the end opposite the mouth. Carefully make a longitudinal cut along the stomach, you
can see the inner lining of the stomach with its many folds and may find some food
reminants.
6. The gonad is the reproductive organ. It is a mass near the far end of the mantle. We
really don’t like to use color as our primary method of identification but the gonad is
white in the male and orange in the female (perhaps even seeing small eggs if part of
the ovary is viewed under the microscope. Compare with your classmates.
What sex is your squid? How did you determine this?
7. Be sure to look at another group that has a squid of the opposite sex, and identify
their sex organs.
8. Locate the gills, two long organs that look feather-like. The gill hearts or brachial
hearts are located at the base of the gills.
9. Probe the mantle near the fins with a probe. Find a hard orange-ish object buried
underneath the thin layer of messentary. Try to remove it in one piece. Grasp this hard
object with the forceps and pull straight out from the body and place it on the dissection
tray. You may need to loosen some of the clear mesentary tissue that holds it into place.
This tough, transparent part is called the pen. It is the shell of the squid.
Why do you think it got this name? (hint—think “old school”)
10. Locate an eye. Make a small cut in the center and find a hard, round object. This is
the lens. Place the lens on the dissection tray.
11. In Figure 2, label the:
water jet, ink sac, stomach, gonad, gill and gill heart.
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12. Mr. Nelson will make his way around the classroom to ask you to identify each of
the following structures. Make sure that each person in the group knows each of these
structures. When your group has finished he will add a secrete
INK SAC
STOMACH
GILL
GONAD
WATER JET
PEN
LENS
COMPLETED!
QUESTIONS
1. Describe the shape of the squid's body.
2. How might the body shape or structure, you describe above, help a squid swim
efficiently?
3. Research to find out how each of the the following help the squid to capture food:
Eyes
Tentacles
Arms
4. Describe how the squid uses its ink sac.
5. Examine a squid. What morphological (structural) characteristics can you see on this
organism that are adaptations to an active predatory existence? List two w/a brief
description of each.
A.
B.
6. Sperm is transferred from the testis to the spermatophoric gland for storage and
packaging (now called spermatophores), prior to ejaculation. Extending from the
spermatophoric gland is the muscular penis which transfers the spermatophores out of
the mantle cavity using a specialized arm called a hectocotylus that he then inserts into
the female's sperm receptacle located in her buccal membrane.
Would this kind of fertilization by the squid be internal or external fertilization?
Explain.