Purpose
To compare and contrast the body plans of annelids
Materials
Preserved Earthworm
Hand lens
Dissection tray
Dissecting pins
Forceps
Scalpel
Probe
Gloves
Microscope
Leach, earthworm CS and nephridium slides
Hand lens
Dissection tray
Dissecting pins
Forceps
Scalpel
Probe
Gloves
Microscope
Leach, earthworm CS and nephridium slides
Method - Part 1: Earthworm (Oligochaeta) Dissection
1. Place earthworm in dissecting tray lined with paper towel and rinse off excess preservatives. Identify the dorsal side, which is the worm`s rounded top, and the ventral die, which is its flattened bottom. Turn the worm ventral side up.
2. Use a hand lens to observe all parts of the worm. Find the anterior end by locating the prostomium, which is a fleshly lobe that extends over the mouth. The other end is the posterior, where the anus is located
3. Locate the clitellum, which extends from segment 33 to 37. Look forn the worm`s setae, which are minute bristle-like spines located on every segment except the first and last ones
4. Locate and identify the external parts of the reproductive system. Find the pair of sperm grooves that extend from the clitellum to segment 15, where one pair of male genital pores is located. Look also for one pair of female genital pores on segment 14. There are more male genital pores on segment 26
2. Use a hand lens to observe all parts of the worm. Find the anterior end by locating the prostomium, which is a fleshly lobe that extends over the mouth. The other end is the posterior, where the anus is located
3. Locate the clitellum, which extends from segment 33 to 37. Look forn the worm`s setae, which are minute bristle-like spines located on every segment except the first and last ones
4. Locate and identify the external parts of the reproductive system. Find the pair of sperm grooves that extend from the clitellum to segment 15, where one pair of male genital pores is located. Look also for one pair of female genital pores on segment 14. There are more male genital pores on segment 26
5. Turn the worm dorsal side up. Using a scalpel and scissors, make a shallow incision in the dorsal side of the clitellum at section 33. Using forceps and scalpel, spread the incision open. Seperate each septum from the central tube using the scalpel, pinning down the skin as you go. Continue the incision foreward to segment 1.
6. Identify the five pairs of aortic arches, or hearts. Then find the dorsal blood vessel. Look for smaller blood vessels that branch from the dorsal blood vessel
7. Locate the digestive tract, which lies below the dorsal blood vessel
8. To locate the organs of the nervous system, push aside the digestive tract and circulatory system. Locate the ventral nerve cord, and trace it back to the nerve collar, which circles the pharynx. Find one pair of ganglia under the pharynx and another pair above the pharynx. The top ganglia serve as the brain of the earthworm.
9. The worms excretory organs are tiny nephridia. There are two in every segment. Locate some of the nephridia.
10. Locate and identify a pair of overies in segment 13. Look for two pairs of tiny testes in segments 10 and 11.
11. Dispose of the worm according to direction from your teacher. Clean up your equipment, sanitize the work surface, and wash your hands before leaving.
Part 2: Other worms
1. Use microscopes to do drawings of the earthworm cross-section, the earthworm nephridium, and the leach, labeling as many structures as possible
2. Draw a diagram of the sandworm (Polychaeta) specimen.
2. Draw a diagram of the sandworm (Polychaeta) specimen.
Results
Earthworm cross-section
Earthworm Nephridia
Leech
Sandworm
Analysis
1. Q: What is the name of the pumping organs of an earthworm?
A: A worm has five aortic arches which it uses as hearts to pump blood through its closed circulatory system
2. Q: In the earthworm, trace the parts of the digestive tract through which food passes.
A: Food enters through the earthworms mouth. It then travels through its pharynx to its esophagus. The esophagus pushes the food through the crop, where it is ground up into smaller bits. It finally enters the intestine, where the food is broken down and all nutrients are absorbed. Any liquid wastes exit through the nephridia, and solid wastes exit through the anus.
3. Q: Which parts of the earthworm serve as its brain? How are these parts connected to the rest of the body?
A: The upper ganglion, below the pharynx, acts as the brain for the earthworm. It is connected to the nerve collar, which is connected to the rest of the body by the ventral nerve cord.
4. Q: Which of the parts of the earthworm that you saw are included in the excretory system?
A: The nephridia dispose of metabolic wastes, such as ammonia, while the anus disposes of any solid wastes.
5. Q: How can you find out if an earthworm eats soil?
A: There will be some dirt left over in the crop of the worm.
6. Q: Among the earthworm`s structural adaptations are its setae. How do you think the earthworm`s setae make it well adapted to its habitat?
A: Since they are found on all sides of the worm, they help it burrow by pushing on all sides of the dirt. They also help the worm to detect its environment
7. Q: How is the earthworm`s digestive system adapted for extracting relatively small amounts of food from large amounts of soil?
A: The crop and gizzard help to grind up the dirt to extract any food from the dirt. All of this then travels through the intestine, where food is absorbed and the remaining dirt is excreted out of the anus along with any other body wastes.
8. Q: Your dissection of the earthworm did not go past segment 32. What will you observe if you dissect the remainder of the worm to its posterior end?
A: The intestine will continue along the body, slowly getting smaller. The ventral nerve cord and dorsal blood vessel will also continue. Eventually, the intestine would end at the anus. You would also see two nephridia per body segment the whole way through.
9. Q: What did each germ layer develop into in the earthworm?
A: The ectoderm formed into the skin of the worm, its septa, and its nervous system. The mesoderm formed the muscle tissue lining the outside of the stomach and the inside of the skin. This muscle aids in speeding up digestion, and a better ability to move around. The endoderm forms all the other organ systems, including the digestive and circulatory systems.
10. Q: What is the function of the nephridium? How does it complete this function?
A: The nephridia are used to remove metabolic wastes, such as ammonia, from the body of the worm. Body fluids enter the nephridium through the nephridiopore, a membrane attatched to the intestine. Once inside the nephridium, any usable water and other liquids are sent back into the body, while wastes are excreted out through tubes along the worms skin.
11. Q: How is the sandworm similar and different to the earthworm?
A: Similar - Both belong to the phylum Annelida. Have identical digestive and circulatory systems, excluding the mouth. Body segments divided by septa. Dispose of wastes using nephridia and anus. Both rely on water to survive.
Different - Sandworm has crude appendages (evolved setae) used for swimming. Around mouth of sandworm are pincers used to trap and kill prey. Sandworm lives in water and breathes through crude gills, while earthworm lives on land and breathes through skin.
12. Q: How is the leech designed to live as an ectoparasite? What are the similarities and differences between the leech and the earthworm?
A: The leech has two different suckers; a head sucker and a posterior sucker. It uses the larger, posterior sucker to latch onto the skin of its prey. It then uses its smaller, head sucker to burrow into the skin and suck the blood of its prey for food and nutrients.
Similarities - Both belong to the phylum Annelida. Have identical digestive and circulatory systems, excluding the mouth. Body segments divided by septa. Dispose of wastes using nephridia and anus. Both rely on water to survive.
Differences - Leaches are parasitic, while earthworms are free-living. Leeches consume blood as food, while earthworms absorb nutrients from food in dirt. Leech lives in water. Leech has two suckers.
A: A worm has five aortic arches which it uses as hearts to pump blood through its closed circulatory system
2. Q: In the earthworm, trace the parts of the digestive tract through which food passes.
A: Food enters through the earthworms mouth. It then travels through its pharynx to its esophagus. The esophagus pushes the food through the crop, where it is ground up into smaller bits. It finally enters the intestine, where the food is broken down and all nutrients are absorbed. Any liquid wastes exit through the nephridia, and solid wastes exit through the anus.
3. Q: Which parts of the earthworm serve as its brain? How are these parts connected to the rest of the body?
A: The upper ganglion, below the pharynx, acts as the brain for the earthworm. It is connected to the nerve collar, which is connected to the rest of the body by the ventral nerve cord.
4. Q: Which of the parts of the earthworm that you saw are included in the excretory system?
A: The nephridia dispose of metabolic wastes, such as ammonia, while the anus disposes of any solid wastes.
5. Q: How can you find out if an earthworm eats soil?
A: There will be some dirt left over in the crop of the worm.
6. Q: Among the earthworm`s structural adaptations are its setae. How do you think the earthworm`s setae make it well adapted to its habitat?
A: Since they are found on all sides of the worm, they help it burrow by pushing on all sides of the dirt. They also help the worm to detect its environment
7. Q: How is the earthworm`s digestive system adapted for extracting relatively small amounts of food from large amounts of soil?
A: The crop and gizzard help to grind up the dirt to extract any food from the dirt. All of this then travels through the intestine, where food is absorbed and the remaining dirt is excreted out of the anus along with any other body wastes.
8. Q: Your dissection of the earthworm did not go past segment 32. What will you observe if you dissect the remainder of the worm to its posterior end?
A: The intestine will continue along the body, slowly getting smaller. The ventral nerve cord and dorsal blood vessel will also continue. Eventually, the intestine would end at the anus. You would also see two nephridia per body segment the whole way through.
9. Q: What did each germ layer develop into in the earthworm?
A: The ectoderm formed into the skin of the worm, its septa, and its nervous system. The mesoderm formed the muscle tissue lining the outside of the stomach and the inside of the skin. This muscle aids in speeding up digestion, and a better ability to move around. The endoderm forms all the other organ systems, including the digestive and circulatory systems.
10. Q: What is the function of the nephridium? How does it complete this function?
A: The nephridia are used to remove metabolic wastes, such as ammonia, from the body of the worm. Body fluids enter the nephridium through the nephridiopore, a membrane attatched to the intestine. Once inside the nephridium, any usable water and other liquids are sent back into the body, while wastes are excreted out through tubes along the worms skin.
11. Q: How is the sandworm similar and different to the earthworm?
A: Similar - Both belong to the phylum Annelida. Have identical digestive and circulatory systems, excluding the mouth. Body segments divided by septa. Dispose of wastes using nephridia and anus. Both rely on water to survive.
Different - Sandworm has crude appendages (evolved setae) used for swimming. Around mouth of sandworm are pincers used to trap and kill prey. Sandworm lives in water and breathes through crude gills, while earthworm lives on land and breathes through skin.
12. Q: How is the leech designed to live as an ectoparasite? What are the similarities and differences between the leech and the earthworm?
A: The leech has two different suckers; a head sucker and a posterior sucker. It uses the larger, posterior sucker to latch onto the skin of its prey. It then uses its smaller, head sucker to burrow into the skin and suck the blood of its prey for food and nutrients.
Similarities - Both belong to the phylum Annelida. Have identical digestive and circulatory systems, excluding the mouth. Body segments divided by septa. Dispose of wastes using nephridia and anus. Both rely on water to survive.
Differences - Leaches are parasitic, while earthworms are free-living. Leeches consume blood as food, while earthworms absorb nutrients from food in dirt. Leech lives in water. Leech has two suckers.