Locomotion. Squid are among the fastest invertebrates on earth speeding through the water at up to 40 km/h (24 mph). Very odd when compared to other members of the phylum Mollusca like the snail, slug, oyster, etc. When escaping predators, some squid can even jump 3m (about 12ft) out of the water and glide like a flying fish. They can move fast because they are naturally jet propelled. The outside body of the squid is called the MANTLE which fits like a hat over the real body and organs of the squid. By opening up the mantle around the head squid suck water inside the mantle. Then they squish the mantle closed. The water is let out in only one place, the FUNNEL. Like a jet fighter engine nozzle, the squid can open, close, twist, and turn the funnel to go where they want. Of course they would fly around like a released balloon if they didn't have FINLETS to act as rudders on the outside. Also like a balloon they would flop and fold if they didn't have a strong support beam, called the PEN inside the mantle to make it stiff.

Breathing/Respiration. Squid live in the ocean, therefore they need some type of gill(s) in order to get oxygen from the water. Oxygen needs to pass from the water into the blood. Squid do this by putting the blood next to the water with only a thin wall, one cell thick, between water and blood in a feathery structure called the CTENIDIUM (two are called CTENIDIA). The ctenidia are found on either side of the siphon. Oxygen-rich water is continually pushed past the ctenidia by contraction of the MANTLE. Some rare, deep-water squid that swim using webbed arms don't have gills, the webs are so thin that they work as gills.

Eating. Squid are very successful predators. They feed on fish, shrimp, just about anything swimming that's smaller than them. Squid have eight ARMS and two TENTACLES, unlike octopus which only have eight arms. The arms are short. They rip-apart prey and stuff it into the mouth in the center of them. The tentacles are much longer and have suckers only at the ends. Squid get close to prey, then shoot out the extra-long tentacles to capture it and pull it in. The squid takes bites out of the prey with a BEAK made out of the same stuff as human fingernails. The meat is ripped apart even more by the RADULA, a conveyor belt of tiny teeth that nearly all molluscs have.
Food is swallowed and travels through the ESOPHAGUS into the small muscular STOMACH where digetive juices from the LIVER and PANCREAS help break it down. The mushy food is then passed into the big CECUM where it is absorbed into the squid's hemolymph (blood) and spread through the body. Wastes are passed out the rectum, through the funnel, and into the water as the squid squirts away.

Reproduction. Most squid live only a short time, one to three years. A male squid makes sperm with a single TESTIS and then wraps it into a packet of sperm called a SPERMATOPHORE with a gland called NEEDHAM'S SAC. He hands it off like a football to the female using his long tentacles. The spermatophore is stuck to the inside wall of the female's mantle so she can use it to fertilize her eggs when she lays them. Often the female doesn't wait for the male to remove his tentacle and she rips it off during her escape. This doesn't affect the male too much because he dies after mating. Female Loligo sp. squid lay from 1000 to 5000 eggs in strings or 'fingers' stuck to the bottom of the ocean. She has two glands, nidamental glands, that make a hard, bad-tasting covering for the egg finger so that other animals won't eat the eggs. After laying her eggs, the female usually dies. Squid usually swarm to shallow water with sandy bottoms to reproduce so when they all die on the bottom seals, sea lions, crabs, humans, and fish harvest the bodies for food. After several weeks baby squid, about the size of a rice grain, hatch out and head to deep water to feed for one or two years before returning to mate and die.

Circulation. Most molluscs (clams, oysters, scallops, snails, and slugs) have an open circulatory system, meaning that the organs slosh around in a single pool of bluish 'blood' called HEMOLYMPH. The fast paced life of a squid is possible partly because its hemolymph is pumped quickly around the body inside veins, arteries, and capillaries; a closed circulatory system like humans have. Earth squid have three hearts. One big SYSTEMIC HEART pumps hemolymph around the body and to the brain, while one BRANCHIAL HEART on each gill helps push hemolymph through the little capillaries there.

Nervous System. Squid have a fairly large brain between their big eyes. The largest parts of the brain are the parts related to vision. Since squid have a soft body (not protected by shells like its relatives clams, oysters, and snails) the brain is protected by a rubbery box almost like a skull made out of cartilage. Humans studied squid brains and nerves for a long time because squid nerve cells are some of the largest on the planet, much bigger than human nerve cells. Two really big ones called STELLATE GANGLIA control the quick squeezing of the mantle. They are so big that humans were able to figure out how nerves work by changing the chemicals and electrical impulses in these nerves. This research led people to develop ways to fight some human diseases like muscular dystrophy, muscular sclerosis, and Alzheimer's.

Research indicates that squid cannot smell, and they have no noses. They can feel different textures, but cannot tell one shape from another. They 'hear' by sensing vibrations in the water. Their eyes, however, are marvelous. Squid eyes are very similar to fish eyes. Squid use their eyes to find and capture prey. They have no eyelid, but control the amount of light coming into the eye by opening and closing their slitted pupil. They focus on something by moving a hard, clear LENS back and forth within the eye. Some species of squid may be able to see color.

Changing Color. The color of a dead squid is very different from the changing colors of a live squid. Color cells, called CHROMATOPHORES, in the squid's skin contract and expand to produce different colors and patterns. Sometimes squid use this ability to hide, but most times their color reflects their moods. Squid can turn dark, squeeze ink out of their INK SAC, then turn light or clear to confuse a predator and escape. Squid ink is made out of melanin (the same stuff that produces human tans) and mucous (snot). Chemicals in the ink also confuse fish noses to help squid get away. Some squid can even glow in the dark, called BIOLUMINESCENCE. Glowing squid use PHOTOPHORES to produce more or less light. For more information on how squid change color, click here.

Information from:
Barnes, R.D., Ruppert, E.E. (1994) Invertebrate Zoology; Sixth Edition. Saunders College Publishing; Harcourt Brace College Publishers. Fort Worth, Texas, US. pages 460-485.

Objectives:

As a result of this lesson, students will be able to:

Describe the physical and biological characteristics of the planktonic, benthic, and nektonic regions of the oceans.

SC.F.1.4.1 know that the body processes involve specific biochemical reactions governed by biochemical principles.

SC.F.1.4.2 know that body structures are uniquely designed and adapted for their function.

Compare the diverse characteristics of representatives of the major phyla/divisions represented in marine systems.

SC.G.2.4.3 understand how genetic variation of offspring contributes to population control in an environment and that natural selection ensures that those who are best adapted to their surroundings survive to reproduce.

Materials:

squid, dissecting kit, dissecting pan, paper towels, microscope, dissecting scope, slides, slide covers, paper

Links

Giant Squid dissection

First Live Giant Squid video

Live Giant Squid video

"Elbow" Squid

Procedure

1. Orientation:

Place the squid with the dorsal (back) side up in the dissecting pan. This means put the side with the funnel down and the fin side up. Make sure the tentacles and arms are towards you. Locate the head, eyes, beaks (mouth), arms (8), two longer feeding tentacles, fins, mantle, and skin. Use the hand lens to examine the suckers on the tentacles and arms as well as the spots on the skin, which are chromatophores. of a squid dissection.

How to use a monocular microscope, make a wet mount slide, and make sketches.

(1) Make a wet mount slide of an area of skin with chromatophores. Using a compound microscope, examine the area of carefully and sketch what you observe. (2) Why are the chromatophores important to the squid? (3) What is the function of the fins?

Click here for labeled photos of this portion of the lab.

GET A STAMP BEFORE PROCEEDING.

Using the dissecting microscope, examine suckers from both an arm and a tentacle (4) What are the differences between arm and tentacle suckers? (5) Why are they different? (6) How is the arrangement of suckers on the tentacles and arms an advantage for the squid?

Click here for labeled photos of this portion of the lab.

GET A STAMP BEFORE PROCEEDING.

2. The Mouth and Beaks:

Locate the dark beaks in the center of the mouth.
Open and close the beaks, noting how the ventral beak overlaps the dorsal beak. (7) How is this different from a parrot's beak? Before you pull out the beaks, imagine what they will look like on the inside. With forceps, remove the beaks and place beaks together with dark pointed parts opposite one another. Manipulate them (open and close) as if the squid were eating. (8) What makes them work in this way? In order to remove the radula (a ribbon with rows of teeth on a tongue-like muscle) from inside the mouth, make small incisions in the edge of the mouth. With tweezers, locate the small, folded, plastic-like radula between beaks and remove it. It is usually very small, yellow or white in color. (9) What is the radula's function? How are squid mouths and beaks like your jaw and teeth? How are they different?

Click here to view a labeled diagram of the buccal mass.

Click here to view a labeled diagram of the anterior internal anatomy.

Store the radula and the beaks in water in a small cup for later microscopic examination.

Drawing of Squid Radula

GET A STAMP BEFORE PROCEEDING.

3. Funnel:

Turn the body over, ventral side up, and locate the funnel (a deflated fleshy tube located at the base of the head). A squid swims by squirting water from the mantle through the funnel. The direction it swims depends on which way the funnel is aimed. Move the funnel and note its flexibility.

(10) How does the squid use the funnel and mantle for locomotion? (11) What is the function of the waterjet?

Click here for labeled photos of this portion of the lab.

GET A STAMP BEFORE PROCEEDING.

4. External Anatomy:

Orient the squid so that the tentacles are away from you, at the top of the dissection tray. Spread out the arms, tentacles, and fins. (12) Draw and label the external parts of the squid: arms, tentacles (have suckers only at the tips), head, eyes, fins, mantle, funnel, tail, suckers, beaks (where each would be found on an intact squid) and mouth. If something cannot be seen, draw an arrow to show where it should be.

Slice open an eyeball and locate the lens, pupil, retina, and iris (colored part of the eye). Examine these using the binocular microscope. Save to show your teacher. Look for the creamy white brain between the eyeballs. For assistance in identifying these parts, refer to the illustration below.

Diagram of cephalopod eye

GET A STAMP BEFORE PROCEEDING.

5. Internal Anatomy

Opening the Mantle:

Keep the squid on its back (the side opposite the funnel). Using forceps, lift up the opening to the mantle behind the funnel (near the head) and separate the mantle from the internal organs. Close the forceps firmly so as to "pinch" the mantle flesh to keep it taut, cut along the ventral midline of the mantle, from its opening all the way to the tail. Be careful to keep the scissors lifted away from the internal organs so they are not damaged.

Locating and Removing Reproductive Organs:

Locate the gonad (reproductive organ) in the posterior end (refer to diagram for shape and location).

      Click here to view male anatomy               Click here to view female anatomy.                                                           

Upon opening female specimens, the large, firm, white nidamental glands are seen first. Males do not have nidamental glands. The glands lay on top of the other internal organs. These glands create the gelatinous matrix that envelops the eggs. In order to proceed further, carefully remove these glands.

In females the eggs are jelly-like in a conical sac at the posterior end of the mantle. The male genital duct is a white, fluid-filled sac in the posterior end of the mantle. The sperm are stored in thin tubes in an elongated sac behind and along one gill.

(13) Explain how squid reproduce. (14) What sex is your squid? How can you tell?

Gills:

Find the gills. These are the long, feather-shaped organs that are attached to the sides of the mantle and extend along the anterior half of the mantle. Identify the gill hearts, one on the posterior end of each gill (these are small, flat and white). (15) Why are they white and our hearts are red or purple? The squid has a third heart (the systemic heart) that pumps blood to the rest of the body. (16) Why does it have separate hearts for the gills alone? (17) How does the squid obtain oxygen from the water?

Click here to view internal anatomy showing the gills.

Digestive Tract:

The long, silvery dark tube on the bottom of the liver (but appearing to be on top of the liver because of the squid's inverted position) is the ink sac. Be careful not to break it open. Locate the stomach and caecum. These lie together as one white, silky-looking tube, like a deflated bladder and a coiled sack.

(18) Open the stomach and examine its contents. Describe what you find.

The bunched up organs that look like human intestines are digestive ducts for the squid. If you are curious about the liver, wait to cut it open until the end of the dissection. It contains a lot of brown, oily liquid which may obscure other organs. Many squid will have bits of partially digested crustaceans (pink and white pieces), or tiny fish scales and bones.

GET A STAMP BEFORE PROCEEDING.

Removing the Ink Sac:

Find and carefully remove the silvery-black ink sac that lies connected to the intestine. To do this, pinch the opening of the sac (near the back of the funnel) with forceps while gently pulling up and cutting the connective membrane along its length. After cutting about 1/3 to 1/2 of it, hold the sac with your fingers and pull the sac off the liver. Be careful not to puncture it. Squid ink stains clothing and skin. Place the sac in a small cup for later use with the gladius (pen).

(19) Where does the ink sac empty into and what is its function?

Removing the Gladius (Pen):

The gladius is a long, clear feather-shaped structure used to support the mantle and for organ attachment. It and the cranium, or brain case, make up the "skeleton" of the squid. It feels like plastic and is made of tissue similar to a shrimp shell.

There are two ways to remove it: from the tail or from inside the cut-open mantle. To remove it from inside the open mantle, grasp the head and organs firmly, and rotate them to the side with your left hand while holding on to one side of the mantle with your right hand and pulling away gently. Pulling the gladius out is like removing a splinter from your skin. You may need to cut away connective tissues that hold the gladius in place.

The gladius is revealed, lying along the dorsal midline of the mantle.

Grab the forward end of the gladius and pull it carefully from its slot in the mantle. It may be helpful to have one person hold down the lower mantle while the other removes the gladius.

To remove from the tail end, rotate the organs to one side, cutting connective tissues. Make sure the mantle is slit along the internal dorsal midline all the way to the tip of the tail. Pry out the tail end of the gladius and pull straight back, away from the body.

(20) What is the function of the pen?

(21) Draw, label, and identify the function of the following internal parts of the squid:

stomach, caecum, hearts (systemic and gill), gills, reproductive organs, ink sac, liver (digestive gland), gladius, brain, eyeball

GET A STAMP BEFORE PROCEEDING.

6. Writing with the Gladius (Pen) and Squid Ink:

Cut one end of the ink sac open and press it against the bottom of the cup with forceps or toothpick. You can also hold one end and push the ink out with your finger, as you would toothpaste from a tube. This will release the ink. Dip the pointed tip (the anterior end) of the gladius into the ink, filling the tip with the dark fluid. (11) Then, using only the ink-filled tip of the gladius, write your name on your squid illustration or paper. If there is enough ink, create and write the name of your dissected squid under its picture. If the ink seems dry and pasty, add one drop of water at a time to create fluid ink. Though this is an unusual way to write, squid ink was actually used to write and draw in ancient times, and it is used today in some cultures. Unfortunately, it tends to fade over time (except from your clothes!).

When finished, clean your area completely. Return all equipment and wash your hands. The squid odor will remain for a little while. Lemon juice will alleviate the odor if you find it offensive. To dispose of your specimen, close it in a zip-lock bag and give it to Mr. Black to freeze for fish food.