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Squid Dissection

Background Information:

The squid is one of the most highly developed invertebrates.

It is in the phylum Mollusca, which is derived from the Latin word meaning “soft body”. It belongs to the

class Cephalopoda, meaning “head-footed”, because its head is pushed down toward the foot. This class

also includes the octopus, cuttlefish and ancient nautilus.

Squid can be as small as a thumbnail, or as large as a house. The giant squid,

Architeuthis, can measure 60 ft. in length and weigh three tons! All mollusks have a soft body with a

special covering called the mantle, which encloses all of the body organs. Squid have a large mantle, eight

arms with two longer feeding tentacles all with suckers, a beak and mouth, a siphon, a large head (with

a brain), two large eyes, and three hearts. The shell has been reduced to a small internal pen that is

embedded in the upper surface of the mantle.

Squid breathe using gills. They move by squirting water from the mantle through the

siphon, using a type of movement called jet propulsion. They can move both backward and forward just

by changing the direction of the water flow through siphon.

Squid can change the color of their skin to mimic their environment and hide from

predators. When in danger, squid release a cloud of dark sepia from their ink sac in order to

confuse their attacker and allow the squid to escape.

These fast-moving carnivores catch prey with their two feeding tentacles, then hold the

prey with the eight arms and bite it into small pieces using a parrot-like beak. The esophagus runs

through the brain, so the food must be in small pieces before swallowing. Squid feed on small crustaceans,

fish, marine worms, and even their own kind!

Squid reproduce sexually by releasing eggs into the water or being fertilized internally. After

mating, a female squid will produce 10-50 elongated egg strings, which contain hundreds of eggs in each

string. In many species, the parents will soon die after mating. The egg strings are attached to the ocean

floor, are left to develop on their own, and hatch approximately ten days later.

Squid are an important part of the ocean food web. Squid are a major food source for

many fishes, birds and marine mammals. Squid are gaining popularity as a food source for humans

around the world (calamari). However, over-fishing is a growing concern because there are no

regulations on squid harvesting. About 6,000 metric tons are taken yearly for human food and bait.

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Dissection Procedure:

Part 1- External Anatomy *DO NOT MAKE ANY CUTS YET!!!

1) Place the squid on the dissection tray so its eyes are facing upright. Squid have big eyes compared to their head. In comparison, humans’ eyes would be the size of dinner plates if the proportion were the same. They are positioned on the side. Being on the side gives them more peripheral vision, which is great for hunting. Label the eyes on the squid diagram.

2) Locate the mantle. The mantle is the main part of the squid’s body—all organs are inside. Label the mantle on the squid diagram.

3) Notice the chromatophores, “freckles” on the squid’s mantle. Chromatophores allow the squid to change colors for camouflage. Try rubbing them to see if you can see a change. Draw & Label the chromatophores on the squid diagram.

4) Locate the fins located on the top of the mantle. These help squid change direction when swimming. Label the fins on the squid diagram.

5) Locate the siphon (a.k.a. funnel) at the bottom of the mantle above the eyes. Water is pulled into the mantle. Than the mantle is squeezed forcing water out through the siphon. This type of movement is called jet propulsion. Squids are the fastest invertebrates swimming at approx. 25 mph. Label the siphon on the squid diagram.

6) Locate and count the number of tentacles the squid has. The tentacles are longer than the arms and have suction cups only at the tips. These are used to pass food to the shorter arms and then to the mouth. Label the tentacles on the squid diagram.

7) Locate and count the number of arms the squid has. Arms have suction cups all the way down. The suction cups help the squid to hold onto food. Label the arms on the squid diagram.

8) Hold your squid like a flower, let the arms lay back so you can see the mouth. Look and try to find the beak. The beak is hard and is a dark brownish color. If there is time later, we will try to extract the beak. Label where the mouth/beak would be on the squid diagram.

9) When you have your external squid anatomy diagram completed, show your instructor, and they will give you a dissection kit to complete the internal anatomy section.

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Part 2- Internal Anatomy *MUST SIGN OUT A DISSECTION KIT!!!

1) Find a soft spot and gently cut the mantle with scissors starting at the bottom and moving UPWARDS to avoid puncturing internal organs. Pin the open flaps of mantle to your dissection tray.

2) Locate and remove the gills from the body. The gills are feathery-looking structures that absorb oxygen from the water. Label the gills on the squid diagram.

3) Locate the 3 hearts inside the squid – 2 branchial (smaller) and one systemic (larger). The hearts are located at the bottom of the gills and used for blood circulation. Label the hearts on the squid diagram.

4) Locate the gonads inside the squid. This is the reproductive organ found above the hearts towards the top of the mantle. In males, it is a whiteish mound (sperm sac) and in females, it is clear to yellow/orange mass of eggs. Label the gonads on the squid diagram & try to identify the sex (male or female).

5) Locate the esophagus inside the squid. This is the tube that connects the mouth to the stomach and will be found at the lower end of the mantle above the siphon. Label the esophagus on the squid diagram.

6) Locate the stomach at the top of the esophagus near the gills. The stomach is where food is digested. If there is time at the end, you may cut open the stomach to see if there is anything inside. Label the stomach on the squid diagram.

7) Locate the ink sac near the stomach. Do NOT pop it until the end of the dissection! The squid releases ink from this gland in times of danger, which is then pushed through the siphon. Label the ink sac on the squid diagram.

8) Locate the intestine tube at the bottom of the stomach & near the ink sac. The intestine leads to the anus where waste is removed from the squid. Label the intestine and anus on the squid diagram.

7) Place your fingers on your mantle and locate the pen (small internal shell). It will feel harder than the soft mantle. Carefully remove the pen from your mantle and show your instructor. Label where you found the pen on the squid diagram.

8) Finally, take the pen, dip it into the ink sac, and sign your initials on your paper.

*If there is time you may:

9) Remove an eye and examine the hard lens inside.

10) Remove the beak and examine the radula.

11) Pop the stomach and examine the contents.

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Part 3- Clean Up *MUST CLEAN UP TO RECEVE CREDIT!!!

1) Throw all squid pieces in the large trashcan. Do NOT throw away any tools!

2) Take your dissection tray and tools to a sink and SCRUB with soap and water!

3) Dry your dissection tray and tools with a paper towel.

4) Leave your dissection tray on the counter for the next class.

5) Return your dissection tools to your instructor. *MUST sign back in to receive credit!

6) Clean your station with a Lysol antibacterial wipe.

7) Throw away your gloves & wash your hands.

Part 4- After Lab Questions

1) What phylum and class are squids a part of?

2) How do squids move around?

3) What special adaptation does a squid have to get away from predators?

4) How do squids capture & eat their prey?

5) How does a squid reproduce?

6) What are 2 reasons squids are important to their environment?

* Make sure both the internal and external anatomy diagrams are labeled, and submit with these after lab questions!