Annelid Dissection

On friday in class, we were allowed to dissect an earthworm as a part of group assignment. This was one of the coolest things we've done all year, apart from the Aquarium trip! The purpose of this dissection was to get a hands on experience of the external and internal structures of an annelid. With experiences such as dissecting, one can retain information better from the things they see, and it can provide a better learning environment. Our class had just finished learning about Annelids, and what better way to keep that information than being active! From the start of the class, we were given some brief precautions and instuctions, and the we were able to get started. Using scalpels, forceps, pins and other various tools, my group and I began our dissection, starting with the head of the worm and lightly slicing toward the centre. Once we had done this, black ooze (soil) fell out from inside of the worm, along with blood, which did kind of disgust me, considering it's not something I see everyday. There was a faint odor that didn't smell too good either, but you had to lean in close to really breathe it in. At this point, you could see the insides of the worm, and under a microscope could see he internal organs of it, all of which looked squishy and sticky. Following all of this, we then cut further down, and sliced open the bottom half, revealing the excretory and reproductive systems. There wasn't much there besides the ovaries, testes and nephridia, and some soil as well. This whole lab was an amazing new experience that I hope everyone else enjoyed as much as myself! Although touching the worm wasn't exactly an option for me, because I have cuts on my fingers, it was still an awesome lab to participate in. Using a scalpel and slicing open something is always a cool experience, so I was glad to be there on friday!

1.) What is the name of the pumping organs of an earthworm?

The name of the pumping organs of an earthworm is called the Aortic Arches.

Although I couldn't get a clear picture of them, hopefully these "hearts" (black orbs) will suffice.

2.) Trace the parts of the digestive tract through which food passes.

This is a picture of an Annelids digestive tract, that I drew myself.

3.) Which parts of the earthworm serve as it's brain? How are these parts connected to the rest of the body?

The brain is made up of many nerves, all through cephalization. The brain rests above the gut, and is connected to 2 large nerves which are, in turn, connected to a pair of ganglia. These ganglia are then connected to a ventral nerve cord which runs the length of the body.

4.) Which parts of the worms body that you saw included the excretory system?

This was the only close up picture I could get of what the excretory system looks like. There appears to be a lot of soil in the mix, as well as some reproductive organs.

5.) How can you find out whether an earthworm eats soil or not?

The black muck that surrounds the pin is the undigested soil, that was once travelling through the worms digestive tract.

6.) Among the earthworms structural adaptations are it's setae. How do you think the earthworms setae make it well adapted to its habitat?

I couldn't get a picture of the Annelids setae because they were too small. As for the question, The earthworms setae make it well adapted to it's environment because they help it feel around the soil, as well as for vibrations in the surrounding area, essentially helping the, escape predators. The setae also help with avoiding obstacles.

7.) How is the earthworms digestive system adapted for extracting relatively small amounts from large amounts of ingested soil?

The food ingested goes through the digestive tract, going down the esophagus until it reaches the crop and gizzard. The crop stores some food, while the gizzard grinds it up into smaller pieces. These small pieces are then finally digested. This process shows how worms digestive systems are adapted for extracting small amounts of food from large amounts of soil. This picture is of the Crop, unfortunately I couldn't get one of the gizzard.

8.) Your dissection of the earthworm did not go beyond segment 32. What will you observe if you dissect the remainder of the worm to it's posterior end?

If I had dissected beyond segment 32, I would find digested food, blood and the ventral nerve cord, which runs the length of the body. I would then find the anus and nephridia. This picture is of the lower half of the dissected earthworm, whose guts and soil were splattered around it, and inside it.

9.) During mating, two earthworms exchange sperm. Fertilization is external, and cocoons are produced from which the young eventually emerge. Refer again to steps 5 and 11, where you located the Earthworms reproductive organs. Use a reference to identify the role of each organ in the reproductive process of the earthworm. On a separate paper, summarize your findings.

Summary: To reproduce, earthworms attach themselves to one another, and then excrete sperm into each other. The sperm is then stored in special sacs, awaiting for the eggs to be ready for fertilization. When the eggs and sperm are ready, the clitellum secretes a sticky ring, in which both the eggs and sperm can fertilize in. If you look closely at the end of the worm, you can see the reproductive organs, or whats left of them.