A Walk With Biology: Worm Dissection

Have You Ever Dissected an Earthworm?

You see them in the dirt, or composes. They are the stars in the movie, "How to Eat Fried Worms?" Some are found under the sea , others have been seen on "Fear Factor" or in murky ponds. If you guessed Annelids, you are correct. In this phyla there are three major classes called: Class Oligoshaeta, better known as earthworms, Class Hirudinea, the leeches, and Class Polycheata, the Marine worms.in the dissection, we chose to dissect an earthworm. We got to use tools such as a scalpel tongs and pins to open up the earthworm to expose the innards. The purpose of this dissection was to help us further learn the parts of an annelid. Using this hands on technique, I find it easier to understand and further learn the different parts of an annelid. This dissection help us understand the biological world because with the visual aspect, we saw what a real earthworm looks like, what it's food looks like, and an up close look at the parts in the annelid. We also got to exercise our dissection skills which will be useful for further dissections. All in all, I had a great time with dissection and look forward to others in the future.

Discussion Questions:

The pumping organs of the circulatory system are called the five aortic arches. The circulatory fluid, also known as hemoglobin,travels through the arches of the ventral blood vessel to the capillary beds in the body. Then, the hemoglobin runs back through the dorsal blood vessels and back to the arches.

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It was quite tough to uncover the digestive tract of the worm; however, food travels through the mouth, into the pharynx, to the esophagus where it travels into this sac like structure called the crop, then a bigger sac like structure called the gizzard. Then, the food travels down the intestinal tube and out the anus.

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Little more of a clear picture of an Earthworm digestive track

The nervous system are made up of a ventral nerve cord. It travels the length of the worm on the ventral side. Ganglia also are included in the nervous system. They are masses of tissues containing many nerve cells. Also, there is a nerve collar that surrounds the pharynx along with ganglia. This ganglia is found both above and below the pharynx. Even though the earthworm's nervous system isn't as advance, the earthworm still responds to stimuli and are responsible for movement.

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Some parts found in the dissection that are apart of the excretory system include the nephridia. They are found in pairs in each body segment. The anus is the last step of the excretory system where the waste it excreted.

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We can find out if a earthworm eats soil by dissecting it. In the dissection, we found dirt in the digestive tracks...

Magnified Soil in digestive track

YUM YUM SOIL

Each segment or section contain muscles and bristles called setae. Setae help anchor and control the worm when moving around it's environment The setae hold a section of the worm firmly into the ground while the other part of the body moves forward.

Once the soil passes through the esophagus, calciferous glands release calcium carbonate to get rid of the excess calcium in the earthworm's body. The food moves into the crop where it is stored and then eventually moves into the gizzard. The gizzard uses stones that the earthworm eats to grind the food completely. That's how big parts of soil become little digestible particles.

Better shot of a Gizzard

We continued to dissect the rest of the worm and when we did, we found the rest of the digestive tract, soil and the anus.

In the reproductive system, the ovaries, clitellum, testes and sperm all make up this system. In our dissection, we figured out how earthworms mated. We also found the ovaries and where this "egg cocoon" constructs itself during and after mating. During mating, two worms line up from each other so sperm can be exchanged. The earthworms each have two male openings. These take in the sperm from another mate. The earthworms have a pair of ovaries that produce eggs. The clitellum will form a slime tube around itself and fill with an albuminous fluid. As the earthworm passes through the slime tube, it will pass over the female opening and pick up the eggs. The tube will continue to move down the earthworm and go over the male opening which has sperm. The eggs will fertilize and the slime tube will close off as the worm moves completely out of the tube. Then, baby worms are formed in time.