LAB: SQUID DISSECTION
MATERIALS:
Dissecting pan Squid specimen Pins Petri dish (optional) Probe(s) paper towels Scissors
PROCEDURE:
Part I – External Anatomy:
1) Determine the dorsal (back) side of the squid by looking for darker coloration and the presence of fins. This is called counter- shading: one side of the body is darker than the other.
2) Notice the chromatophores. The “freckles” allow the squid to change colors. These spots change size to change the squid’s color for camouflage. Try rubbing them to see if you can see a change. The fresher a specimen is, the more likely you will see a change. On the External Squid Diagram (#1) draw and label some chromatophores
3) Find the fins. These help squid change direction when swimming. Label these on diagram #1
4) Locate the mantle. The mantle is the main part of the squid’s body—all organs are inside. Label the mantle on diagram #1.
5) Locate the eyes. Squid have relatively big eyes compared to their head. In comparison, humans’ eyes would be the size of dinner plates if the proportions were the same. They are positioned on the sides of the head. Being on the side gives them better peripheral vision, which is great for hunting in an aquatic environment. Label the eye on diagram #1.
6) Stretch out the arms so that you can count them and locate the two longer tentacles. Arms have suction cups all the way down. The tentacles are longer than the arms and have suction cups only at the tips. These are used to hold onto food and pass food to the shorter arms and then to the mouth. Label the arms and tentacles on diagram #1.
7) See picture A below: Hold your squid around the mantle like a flower, with the arms/tentacles up. Peel and hold back the arms/ tentacles so that you can see the mouth in the center. You will be able to see the
buccal bulb, it is muscular tissue that surrounds the mouth. The buccal bulb attaches to esophagus, which is attached to the stomach.
8) See picture B below: Look and try to find the beak. With a probe you can feel this hard structure inside the mouth. It is a dark brownish color. The beak may be surrounded by some tissue. If it is, simply pull that back with your forceps to view the beak more clearly. The beak is used to tear prey and can be very sharp (and deadly to fish!). Label the beak in diagram #1
9) Picture(s) C below shows a beak that has been removed; this is difficult and time-consuming to do so we will not be doing this. The long tube coming from the back of the mouth/beak is called the esophagus and leads to the stomach (not shown)
A
B
C
10) Lay your squid ventral (belly) side up; this is the lighter-colored side. Locate the collar. The collar is the opening of the mantle (like the collar of your shirt). Label the collar on diagram #1.
Part II – Internal Anatomy
1) Place the squid on its dorsal side (back, darker-colored) down. Lifting up on the collar, use scissors to cut the mantle UPWARDS towards the fins and through the middle of them. Lift the mantle as you cut in order toavoid puncturing internal organs. Lay the flaps of mantle to the sides – you will need to pin these down. Pin the mantle open so that the inside of the squid can be viewed. You may see eggs if you have a female.
2) One of the more obvious structures on the inside of the squid is the ink sac. It is visible as a dark pouch in the middle of the body near the siphon. The ink sac lies on top of the liver. The squid releases ink from this gland in times of danger; ink is pushed through the siphon and comes out into the water as a dark cloud to confuse predators. Carefully pull up the ink sac with the tip of your scissors or finger and snip the ink sac away from the liver. Set it aside in your pan. Label the ink sac on diagram #2
4) At the top of each gill you will find a heart, this is called a gill-heart. The hearts are for pumping and circulating fluids throughout the body cavity. Squid have 3 hearts total; 2 gill hearts and 1 Systemic.
Label these hearts on Diagram #2
5) The large structure in the middle of the squid is called the nidamental gland. It is more noticeable in female squids.If you lift the nidamental gland, the stomach lies just underneath it. The stomach is often a thin membraned structure that can easily be missed among the other organs of the squid. If you locate the buccal bulbagain and pull on it gently, it will show trail of the esophagus and general
area of the stomach.
7) If you push all of the organs of the coelom to the side, you can see the pen. The pen is a hard structure that is used to stabilize the squid when it is swimming. If you are careful, you can remove it in one piece. The squid is related to other “shelled” animals like clams and snails. The pen is all that is left of the shell the squids’ ancestors once had.
These are pens that have been successfully removed
IF TIME -
•Remove eye and examine it. Remove the cornea (film like), and the lens (hard silvery pearl-like structure)
•Examine the beak and radula under the dissecting microscope
PART III – Clean-Up
1) Remove any pins from the squid and return them to their container.
2) Place squid in the garbage can in the front of the classroom. Scrape out any solid pieces of squid into the trash using your hand or bang the pan against the side of the trash can to remove small pieces. 3) Rinse out the pan with water in one of the big sinks.
4) DRY your dissection pan thoroughly with paper towel.
5) Wipe off any dissecting tools used and return them to your tool box. 6) Wipe table with paper towel if necessary.
