Download Squid (Loligo pealeii) Dissection Lab Background information

Name
Squid (Loligo pealeii) Dissection Lab
Background information:
There have always been folktales about giant creatures with long arms that live
in the depths of the sea. Squid belong to a large group of marine animals called
mollusks. They vary in size from 5 cm. to 6 meters. The giant squid is the
largest of all invertebrates.
Questions:
1. Squid belong to a group called
2. Squid range in size from
3. _________________ is a word meaning sea or related to sea.
Body characteristics of the squid
Squid have a body shaped like a cylinder with a head attached to one end. On
the head there are ten arms. Of these ten arms, two are much longer and have
suction cups near their tips. Below the head is the squids’ body which is covered
by a mantle. On the mantle are two lateral fins. The shell usually associated
with other mollusks is only a tough transparent structure inside the mantle called
the pen.
The circulatory system of the squid is a system of veins and arteries. Their blood
is not based on hemoglobin (which contains iron and makes our blood look red)
but instead is copper based (hemocyanin) which makes their blood appear
green.
Questions:
4. The squid’s body is shaped like a _________________.
5. How many arms do squid have?
6. What is a pen?
7. What color is squid blood?
Why?
Nervous System
Squid have a large brain protected by cartilage-like shields in their head. The
brain is complex and controls the sense organs, body parts and behavior of the
squid. The squid has huge nerve cells that coordinate the mantle and arms.
Questions:
8. The brain controls _____________________, _____________________
and ______________________________.
9. What protects the squid’s brain?
How squid move
Squid are powerful swimmers. Some squid are capable of reaching high speeds
and are able to leap 3 meters above the water. To move they allow water to
enter the mantle cavity, when the mantle is contracted the spaces are closed and
water is forced through a funnel propelling the squid through the water.
Questions:
10. How does water enter the squid’s body?
11. Which part of the body moves through the water first the mantle or the
head?
How do Squid eat?
Squid grasp their prey with the suction cups on their arms, bringing the prey to
their mouths and attack it with their strong beak like jaws. The food is then
broken down by the radula, a toothed organ in their mouth.
Defense
Squid are the favorite food of many sea animals such as fish and sea mammals.
To get away the squid will first release a fluid called ink. This confuses the
attacker and allows the squid to quickly swim away and hide. Squid also have
the ability to change their color to match their background.
Questions:
12. How do squid capture their prey?
13. How do squid keep from being eaten?
Reproduction:
Squid have two different sexes. The male fertilizes the female’s eggs inside the
mantle. The eggs are encased in a gooey mass that hardens when it is released
into the water. Most squid lay one egg at a time. Young squid look like a smaller
version of the adults.
Questions:
14. How many sexes do squid have?
15. Where does fertilization take place?
The Squid Dissection
Materials:
Dissecting scissors, Tweezers, dissecting tray and one squid
Procedure:
With your group do the dissection step by step as given in the directions. Answer
the questions as you go. Label the diagram at the end. When you have finished
your dissection, make sure throw away all parts of your squid, wash your trays
and dissecting equipment and return it dry.

Examine the outside structures of the squid, looking closely at the
arms, head, mantle and lateral fins.
Questions:
1. How many arms are there?
2. Do all the arms have suction cups? If not how many do not.
3. What is covering the mantle?
 Holding the squid’s had and body in one hand, gently separate the
arms to see the squids mouth
 Notice the dark spot in the center of it’s mouth, these are the jaws.
With your tweezers, gently pull on the upper jaw. It will come out
an look like half of a parrot’s beak. Remove the lower jaw as well
and wee how the pieces fit together.
Question:
4. How does the squid use this part of the mouth?

Inside the mouth is the radula. The radula might be compared to
our teeth.
Question:
5. How does the radula help a squid to eat?

Through the mouth, carefully grasp the brain with tweezers. Pull
carefully and a long nerve that travels down the squid’s back will
come out as well.
Question:
6. What do the brain and nerve do for the squid?
 Straighten out the squid’s body and lay it flat on the dissecting pan.
 Notice the pointed part of the mantle near the squid’s head. The
point is on the dorsal side, the underneath side is the ventral side.
 Turn the squid ventral side up, hold the mantle away from the
internal organs and with your scissors cut carefully through the
mantle.
 Lay open the mantle to see the internal organs
 Find the silvery black organ-that is the ink sac!
Questions:
7. What does dorsal mean?
8. How does the squid use his ink sac?
 Locate the esophagus, which is the main tube leading out of the
mouth
 Locate the liver, a pale brownish organ under the ink sac
 Locate the stomach, a white lump about the size of a bean.
 Locate the gonad (reproductive organ), a white gooey mass at the
tail end of the squid
 Locate the gills, two long organs that lie on either side of the middle
Question
9. What do the gills do for the squid
 With your tweezers, gently probe the squid’s fin end. There should
be a hard point. Grasp that point and gently pull
Question
10. What is the structure you just removed?
Write a description of this
structure:

Feel free to see if you can use the pen and ink to write your name
in the space provided on the question sheet
 Remove the lens of the eye. Make a small cut in the center of the
eye and feel around inside the eye for a small, hard, round object
Draw and label the parts of the squid on the back of your question sheet.