Name Date: Block: Honors Marine Biology Mr. Conlan - Squid Dissection Lab Objective: Can you identify a squid s structures and their functions? Helpful Hints Everyone must wear safety goggles during the entire lab. There are only enough gloves for one pair per person. Follow the directions in the lab. Read it very carefully and identify all the parts. Pay attention to the bold words. Use the diagrams to help you identify the structures. After the completion of the lab you will complete an analysis in your journals and for homework. gloves and apron safety goggles dissecting scissors probe Materials dissecting tray dissecting microscope microscope slide forceps External Anatomy - Procedure To study the external anatomy of the squid, you must understand the anatomical orientation of the squid body (Figure 1). Dorsal, ventral, anterior, and posterior surfaces all exist, although they are difficult to recognize. The tentacles and arms of the squid are located on the ventral surface of its body. The long, pointed body tube with the two fins tapers dorsally, so the "tail" is actually the dorsal surface of the body. The siphon or funnel is located on the posterior surface. The fins are attached on the anterior surface. While snails, snakes, and cats move along an anterior-posterior axis, a squid moves along a dorsal-ventral axis. To begin your study, place the squid in a tray with its ventral surface away from you (tentacles are ventral) and its dorsal surface toward you. Place the anterior surface facing up (Figure 2). Page 1
You will first notice that the body is elongate and almost torpedo shaped, with two flared fins attached to the anterior surface. The fins are used in locomotion, acting as horizontal stabilizers and as rudders. In some squid, they also can serve as a means of propulsion. The main portion of the body is the body tube or mantle, a muscular sac surrounding those portions or the body dorsal to the head and foot. Figure 2 External Anatomy squid, this causes rapid color changes. The outer covering of the body tube is the epidermis. Chromatophores are abundant throughout the epidermis. Chromatophores are small membranous sacs filled with pigment. Small muscles are attached to each. Changes in the environment cause the nervous system to stimulate the individual muscles to contract, changing the size of each chromatophore. In living Along the ventral edge of the body tube is the collar. Turning the specimen around so that the tentacles face you enables you to look inside the collar and view the mantle cavity. Projections along the edge of the collar are the articular ridges. These are internal cartilaginous support structures. Running down the middle of the anterior surface is a ridge. Under this ridge lies the pen, the internal "shell" of the squid. Page 2
Located on the ventral end of the specimen is the head region and the highly modified foot. The head contains two well-developed eyes, structurally similar to the eyes of vertebrates-a fine example of convergent evolution. Dorsal to the eyes is the olfactory groove and olfactory crest. A small pore, the aquiferous pore, is located at the ventral edge of the eyes (Figure 4). It probably aids in equalizing pressure. Figure 4 Figure 3 On the ventral end of the head is the foot, which in squid has become modified into eight short arms and two elongated tentacles. Both the tentacles and the arms have suckers on the ventral surfaces-along the entire length of the arms, but only at the distal ends of the tentacles. The suckers are used for capturing and holding prey. Suckers are cup-shaped structures, each attached by a stalk (Figure 3). There are chitinous teeth in each sucker. Turning the squid over with its posterior surface (Figure 5) facing up reveals the siphon or funnel, a cone-shaped structure that extends beyond the collar. The living squid draws water into the mantle cavity. When the mantle contracts, water is forced back out the siphon. The squid moves by water-jet propulsion. The squid can direct its movements by rotating its siphon so the opening points in different directions. The final external structure we will discuss is the mouth, Figure 6 located on the ventral surface. This is easily located by spreading the tentacles apart (Figure 6). Page 3
Figure 7 Inside the mouth are two beak-like structures that rip and tear prey into smaller pieces for swallowing (Figure 7). Internal Anatomy Procedure To observe the internal anatomy, make an incision along the middle of the posterior surface of the mantle, beginning at the collar and stopping at a point close to the apex of the dorsal end (Figure 8). This incision is best made using a pair of sharp scissors. Take care not to cut any of the internal organs. Open to reveal the mantle cavity and rinse with running water to remove any excess latex or other loose materials. Pin the cut edges of the mantle to the dissecting pan. The internal organs should be clearly visible (Figures 9 and 10). The internal anatomy of male and female squid differs; we will point out structures peculiar to one sex or the other as we go through the procedure. Figure 8 Page 4
Figure 9 Internal Male Anatomy Page 5
Figure 10 Internal Female Anatomy The siphon or funnel is now easily seen posterior to and covering a portion of the head. A pair of large muscles is attached to the siphon and runs dorsally. These are the siphon retractor muscles and are used to change the orientation of the siphon, resulting in a change of direction of the jet of water exiting the siphon. Anterior to the siphon retractor muscles are the cephalic retractor muscles, Page 6
which are used to move the head. If the siphon is cut medially and folded back (Figure 11), the siphon valves are revealed. These function in regulating the flow of water through the siphon. Immediately dorsal to the siphon is the anterior or cephalic vena cava. This large vein brings blood back from the head to the venous hearts. It should contain blue latex in an injected specimen. We will discuss more of the anatomy of the anterior vena cava later. Beneath the siphon is the liver, an elongate and highly vasculari:e3 organ. A thin layer of tissue separates the liver from the anterior vena cava. Also present buried within the liver is the esophagus. Dorsal to the siphon is the ink sac, a silvery structure attached to the rectum by mesenteries and opening into the siphon near the anus. The ink sac is filled with a pigment that can be ejected into the water when the squid is disturbed. The pigment rapidly mixes with the water, causing a cloud behind which the squid can escape. Because it is so easily punctured, the ink sac is best left in place. Take special care when moving it to one side so that you do not puncture it. If you should do so, immediately rinse the ink away with running water, as it will make the interior of the specimen difficult to view and will stain any fabric it contacts. On the posterior side of the ink sac is the rectum, with the anus at the ventral end. Lateral to the rectum in males is the penis. In females, the oviduct is present in this position. Before we proceed further dorsally, we should identify the two large, feathery structures lying on either side of the retractor muscles. These are the gills, the respiratory organs of the squid. The gills are attached to the mantle by the gill mantle mesenteries. In the squid, there are two types of hearts rather than one heart with multiple chambers (Figures 13). The paired branchial hearts pump oxygen-poor blood to the gills. In a latex-injected specimen, they are recognized as the pair of spherical blue objects at the dorsal ends of the gills. The systemic heart is located slightly below the base of the gills and pumps oxygen-rich blood. It can only be observed by removing the kidneys. Oxygen-rich blood flows from the branchial veins to the systemic heart and then through the arteries to the organs of the body. Oxygenpoor blood flows through the veins to the branchial hearts and through the branchial arteries to the gills. Now back to what we can easily see. Page 7
Figure 13 Proceed dorsally along the rectum until it appears to join a large, blue, cone- shaped object. This is the nephridial, or kidney tissue. There are actually two triangular kidneys surrounded by a nephridial sac. The sac causes the kidneys to appear as one structure surrounding the anterior vena cava. At the ventral end of the nephridial tissue is a pair of openings, the nephridiopores. The nephridiopores release nitrogenous waste into the mantle cavity where it is expelled through the siphon. Because the walls of the vena cava lie in very close association with the nephridial tissues and are relatively thin and easily torn, it is difficult to distinguish the nephridial tissue from the nephridial portion of the anterior vena cava. Inside this surrounding mass, the anterior vena cava actually splits, with a branch going to each of the branchial hearts. The branchial veins appear to join the nephridial sac, but they actually pass under it to connect with the branchial hearts. As noted previously, the nephridial tissue covers the systemic heart. If your specimen is a female (Figure 10), you will notice that the nephridial tissue is covered by other tissue, the nidamental glands. Nidamental glands produce the coverings for the eggs. Immediately ventral to these are the accessory nidamental glands. Remove both types of glands. The Y-shaped blue structure which appears to join the dorsal portion of the nephridial tissue is actually two separate vessels with nephridial tissue surrounding them. These are the posterior vena cavae, which receive blood from the dorsal end of the body and pass it to the branchial hearts. Page 8
Between the posterior vena cavae are three arteries. A single medial mantle artery lies between the two lateral mantle arteries. These provide the dorsal portion of the mantle with oxygen-rich blood. On the opposite side of the body cavity from the seminal vesicle, you can carefully move aside various organs and locate the stomach. Between and proceeding dorsally to the lateral mantle arteries is the cecum or gastric pouch. Digestion and absorption take place here. The cecum may be large and distended if your specimen has recently taken prey, or small if it has not eaten for some time. Dorsal and lateral to one branchial heart in males is the spermatophoric gland, a part of the male reproductive system. This gland provides secretions that help make up the completed individual sperm. Sperm exit the spermatophoric gland and enter the seminal vesicle, where they are stored until they are released through the penis. Anterior to the cecum is the gonadal tissue. In males this is the testis, which produces sperm, while in females it is the ovary, which produces eggs. Final Dissection 1.) Reach under the squid and remove the pen from the dorsal side by grasping it firmly with your fingers and pulling it free from the mantle. 2.) Examine a single sucker from an arm. a. Cut off a O.5-cm piece of the arm and place it on a glass slide. b. View it under the dissecting microscope. 3.) Observe the chromatophores, small freckle-like spots on the outer layer of the mantle. Cut out or peel off a small piece of the skin that contains the spots. Observe under a dissecting microscope. 4.) Remove the beak. See Figure 18 to help you remove the beak from the head. Page 9
Figure 16 Male Squid Page 10
Figure 17 Female Squid Page 11
Figure 18 Dissection of head showing buccal bulb Page 12