Dissection Lab
1. Starfish
Pre-Dissection:
Pedicellariae: keep the body surface clear of algae, encrusting organisms, and other debris
Ambulacral Spines: used to aid arm in movement
Ambulacral Groove: aid arm in movement
Disk: protects the stomach and other internal organs
Mouth: used for capturing and eating food
Spines: protect the starfish from predators
Anus: expels fecal matter
Arm: used to move
Madroporite :used to filter water into the water vascular system
Post Dissection:
Incision Guide
1. Lay the starfish with its aboral side up.
2. Cut off the tip of a ray and then remove the flap of skin to observe the two long digestive glands called the pyloric caeca.
3. Cut a circular flap of skin from the central disc to observe the stomach.
4. Remove the pyloric caeca from the dissected ray to observe the gonads.
5. Cut off the tip of a ray to observe the parts of the tube feet.
6. Locate the bulb-like top of a tube foot called the ampulla. This sac works like the top of an eyedropper to create suction. The bottom of the tube foot is a sucker.
7. Embedded in the soft body wall are skeletal plates called ossicles.
8. Running down the center of each arm is a lateral canal to which tube feet are attached.
9. In the central disc the five lateral canals connect to a circular canal called the ring canal.
10. A short, canal called the stone canal leads from the ring canal to the madreporite where water enters.
Dissection Video
http://youtu.be/fBDWEHzKHS8
http://youtu.be/fBDWEHzKHS8
2. Clam
Pre-Dissection:
Exhalent Siphon- allows water flow for locomotion, feeding, respiration, and reproduction
Umbo- hinge that allows for the opening and closing of the clam
Post Dissection:
Incision Guide
1. Locate the umbo, the bump at the anterior end of the valve. This is the oldest part of the clam shell. Find the hinge ligament which hinges the valves together and observe the growth rings.
2. Turn the calm with its dorsal side down and insert a screwdriver between the ventral edges of the valves.
3. Turn the screwdriver so that the valves are about a centimeter apart. Leave the tip of the screwdriver between the valves and place the clam in the pan with the left valve up.
4. Locate the adductor muscles. With your blade pointing toward the dorsal edge, slide your scalpel between the upper valve & the top tissue layer. Cut down through the anterior adductor muscle, cutting as close to the shell as possible.
5. Repeat step 4 in cutting the posterior adductor muscle.
6. Bend the left valve back so it lies flat in the tray.
7. Examine the inner dorsal edges of both valves near the umbo and locate the toothlike projections. Close the valves & notice how the toothlike projections interlock.
8. Locate the muscle "scars" on the inner surface of the left valve. The adductor muscles were attached here to hold the clam closed.
9. Identify the mantle, the tissue that lines both valves & covers the soft body of the clam. Find the mantle cavity, the space inside the mantle.
10. Locate two openings on the posterior end of the clam. The more ventral opening is the incurrent siphon that carries water into the clam and the more dorsal opening is the excurrent siphon where wastes & water leave.
11. With scissors, carefully cut away the half of the mantle that lined the left valve. After removing this part of the mantle, you can see the gills, respiratory structures.
12. Observe the muscular foot of the clam, which is ventral to the gills. Note the hatchet shape of the foot used to burrow into mud or sand.
13. Locate the palps, flaplike structures that surround & guide food into the clam's mouth. The palps are anterior to the gills & ventral to the anterior adductor muscle. Beneath the palps, find the mouth.
14. With scissors, cut off the ventral portion of the foot. Use the scalpel to carefully cut the muscle at the top of the foot into right and left halves.
15. Carefully peel away the muscle layer to view the internal organs.
16. Locate the spongy, yellowish reproductive organs.
17. Ventral to the umbo, find the digestive gland, a greenish structure that surrounds the stomach.
18. Locate the long, coiled intestine extending from the stomach.
19. Follow the intestine through the calm. Find the area near the dorsal surface that the intestine passes through called the pericardial area. Find the clam's heart in this area.
20. Continue following the intestine toward the posterior end of the clam. Find the anus just behind the posterior adductor muscle.
21. Use your probe to trace the path of food & wastes from the incurrent siphon through the clam to the excurrent siphon.
Dissection Video
3. Grasshopper
Post Dissection:
Incision Guide
1.Using forceps, remove each of the appendages from the head.
2. Examine the following appendages on the thorax.
3. Using forceps, remove one of the walking legs and identify these parts --- the coxa connects the femur (the thickest part of the leg) to the grasshopper's body; a slender, spiny tibia connects the femur to the tarsal segments (lowest part of the leg).
4. Remove a jumping leg.
5. Raise both pairs of wings and locate the first abdominal segment.
6. Locate the tympanic membrane or eardrum on the first abdominal segment.
7. Using a magnifying glass, locate the spiracles or tiny pores for respiration on each side of the abdominal segments.
8. Determine if your grasshopper is a male or female by looking at the end of the abdomen. Females have a tapered abdomen that ends in a pointed egg laying tube called the ovipositor. Male have a more rounded abdomen that turns upward.
Dissection Video
http://youtu.be/3sCpXPAYYxE
http://youtu.be/3sCpXPAYYxE
4.Crayfish
Post Dissection:
Incision Guide
1. Place a crayfish on its side in a dissection tray. Use the diagram below to locate the cephalothorax and the abdomen. The carapace, a shield of chitin, covers the dorsal surface of the cephalothorax. On the carapace, observe an indentation, the cervical groove, that extends across the midregion and separates the head and thoracic regions. On the thoracic region, locate the prominent suture or indentation on the cephalothorax that defines a central area separate from the sides. Note the individual segments of the abdomen.
2. Turn the crayfish with its DORSAL side upward, and locate the rostrum, which is the pointed extension of the carapace at the head of the animal shown in the diagram above. Beneath the rostrum locate the two eyes. Notice that each eye is at the end of a stalk.
3. Locate the five pairs of appendages on the head region. First locate the antennules in the most anterior segment. Behind them observe the much longer pair of antennae.
4. Locate the mouth. Then observe the mandibles, or true jaws, behind the antennae. Now locate the two pairs of maxillae, which are the last appendages in the cephalic region.
5. On the thoracic portion of the cephalothorax, observe the three pointed maxillipeds.
6. Next observe the largest prominent pair of appendages, the chelipeds, or claws. Behind the chelipeds locate the four pairs of walking legs, one pair on each segment.
7. Now use the walking legs to determine the sex of your specimen. Locate the base segment of each pair of walking legs. The base segment is where the leg attaches to the body. Use a magnifying glass to study the inside surface of the base segment of the third pair of walking legs. If you observe a crescent-shaped slit, you have located a genital pore of a female. In a male, the sperm duct openings are on the base segment of the fourth pair of walking legs. Use a magnifying glass to observe the opening of a genital pore.
8. On the abdomen, observe the six distinct segments. On each of the first five segments, observe a pair of swimmerets.
9. On the last abdominal segment, observe a pair of pointed appendages modified into a pair of uropods. In the middle of the uropods, locate the triangular-shaped telson.
10. Now turn the crayfish ventral side up. Observe the location of each pair of appendages from the ventral side.
11. Remove all jointed appendages of the crayfish.
12. Using one hand to hold the crayfish dorsal side up in the dissecting tray, use scissors to carefully cut through the back of the carapace. Cut along the indentations that separate the thoracic portion of the carapace into three regions. Start the cut at the posterior edges of the carapace, and extend it along both sides in the cephalic region.
13. Use forceps to carefully lift away the carapace. Be careful not to pull the carapace away too quickly. Such action would disturb or tear the underlying structures.
14. Place the specimen on its side, with the head facing left. Using scissors, start cutting at the base of cut line. Extend the cut line forward toward the rostrum (at the top of the head).
15. Use forceps to carefully lift away the remaining parts of the carapace, exposing the underlying gills and other organs.
16. Locate the maxillae that pass the pieces of food into the mouth. The food travels down the short esophagus into the stomach. Locate the digestive gland, which produces digestive substances and from which the absorption of nutrients occurs. Undigested material passes into the intestine. Observe that the intestine is attached to the lobed stomach. The undigested material is eliminated from the anus.
Dissection Video
http://youtu.be/idGeyRXd0OU
http://youtu.be/idGeyRXd0OU
