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Segmented Worms

Introduction

Segmented worms are special because they can do so much stuff with no arms or

legs. They can move without legs. Examples of Segmented Worms are: earthworms,

marine worms and leeches. Actually, the more numerous and typical members of the

phylum are marine, crawling or hiding under rocks, or living in burrows, or in tubes, or in

the sediment. Now I will tell you more information about segmented worms. I hope that

we will learn interesting things through this project.

Segmented Worms Characteristics

Segmented worms (phylum Annelids) are so named because of their elongated,

more or less cylindrical bodies divided by grooves into a series of ring-like segments.

Each segment contains nerve cells and waste-secreting organs. The digestive tract is

not segmented. It is instead a continuous, through and through tube that runs through

all segment walls. Just like the digestive tract, the nerve cord and the two main blood

vessels are also continuous. Each body segment has some small blood vessels that

connect to the two main blood vessels. These worms have a closed circulatory system.

Segmented worms are bilaterally symmetrical (if you cut an earthworm along its vertical

plane, the two resulting halves are identical to each other).

Segmented Worms Habitat

Segmented worms can be found in fresh and salt water. Earthworms can be found at

just about every corner of the earth. They live in trees, bark, and under rocks, and along

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rivers, near springs, and near ponds. Their favorite place to live, however, is in the

earth’s rich soil. During the winter months they burrow deep within the earth until the

surface warms again during the spring. During the warm summer months worms stay

closer to the tops of soil where they create tunnels to wiggle in and out of. These

tunnels are extremely important for plant life as they create a path for water and air,

which is essential for the survival of plant life.

Earthworms Body Systems

Earthworms have a definite front end and backend. They have more than 100 body

segments. Earthworms on the outside of each body segment have a bristle-like

structure called setae. Each body segment has four pairs of setae (except for the first

and last segments). They use their setae to hold on to the soil and to move. The setae,

made of a substance called chitin, are used in crawling or in swimming. They have

bilateral symmetry. Their body is composed of: body cavity that holds the organ and

two body openings: mouth and anus.

Digestion and Excretion

Earthworms get energy from the bits of leaves and other matter found in the soil. The

soil ingested moves to the crop (sac used for storage). Then the gizzard (muscular

structure behind the crop) grinds soil and the bite of organic material. Ground material

passes to the intestine where the organic matter is broken down and the nutrients are

absorbed by the blood. Wastes leave the worm through the anus.

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How earthworms help fertilize the soil

Earthworms take in soil and provide spaces for air and water to flow through it. They

provide and mix the soil. Their wastes pile up at the openings to their burrows. The pile

up is called casting (vermicompost), which helps fertilize the soil.

Earthworms Circulatory System

Earthworms have a closed circulatory system. Two blood vessels along the top of

the body and one along the bottom of the body meet in the front end of the earthworm.

There they connect to heart like structure called aortic arches. Aortic arches pump

blood through the body.

Earthworms Respiratory System

Earthworms do not have gills or lungs. Oxygen and carbon dioxide are exchanged

through their skin. This means, they breathe through their skin, so the worm’s

environment and the worm’s skin must be moist at all times. This allows the worm to

breathe in oxygen. While the sand may be moist and wet closer the water, the majority

of the sand is dry. If the worm’s skin dries out, the worm will die from suffocation. In

addition, too much moisture can also be detrimental to worms. If too much water is

present, it takes the place of oxygen, which will cause the worms to flee to the surface.

Once on the surface, worms will be exposed to sunlight. If worms remain in the sunlight

for too long, they can become paralyzed. It is covered with a thin film or watery

mucous. They do not survive in puddles of water.

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Earthworms Nerve Response

Earthworms have a small brain in their front segment. Nerves in each segment join

to form a main nerve cord that connects to the brain. All major nervous, circulatory, and

digestive organs are located near the head. The posterior segments, which are nearly

identical to each other, contain peripheral structures for all of these systems. This

means that if you cut the worm in half, it will die. However, if you cut the worm near the

posterior portion (a third or less away from the very end) the worm can regrow that

portion of its body. The posterior portion will not grow a new head.

Earthworms Reproduction

Earthworms are hermaphrodites (Produce sperm and egg in the same body). An

individual worm can't fertilize its own eggs. It has to receive sperm from another

earthworm in order to reproduce. They have 2 pairs of testes present in 10th and 11th

segments. They are 2 pairs of seminal vesicles which produce, store and release the

sperm via male pores, and ovaries and ovipores that release eggs via female pores.

Marine Worms (Polychaetes)

There exist more than 8,000 species of marine worms. They float, burrow, build

structure or walk along the ocean. Some of them produce the own light. Marine worms

like earthworms, have segment with setae. On these worms the setae occur in bundles.

One Marine Worm example is Sessile (bottom-dwelling polychaetes) such as Christmas

Tree Worms have specialized tentacles that are used for exchanging oxygen and

carbon dioxide and gathering food. Marine Worms and their larvae are food for many

fish, invertebrates and mammals.

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Leeches

Leeches are segmented worms. Their bodies are not as round or as long as

earthworms are. They don’t have setae, but a sucker at each end of the body. They

feed on the blood of other animals. Leeches can survive by eating aquatic insects and

other organism (but they prefer to eat blood). Sometimes they are used after surgery to

keep blood flowing to repaired area. They produce many chemicals, including an

anesthetic that numbs the wound so you don’t feel its bite.

Value of segmented worms

Earthworms help aerate the soil by constantly burrowing through it. They speed up

the return of nitrogen and other nutrients to the soil for use by plants (by grinding and

partially digesting the large amount of material in the soil). Leeches researchers are

developing drugs based on the chemical that come from leeches because leech saliva

prevents blood clots.

Origin of Segmented Worms

Some scientist hypothesize that they evolved in the sea. Some fossils of tubes of

marine worms date back about 620 million years. Similarities between mollusk and

segmented worms suggest that they could have a common ancestor.

Conclusion

Segmented worms have great ecological importance in our habitats. They help us

because when they dig through the soil the help the plants with those holes so water

and nutrients can go to the hole and when plant roots reach there they get the nutrients

that are in the hole. That keeps the plants alive and that means they give oxygen and

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we can breathe. Also their waste helps the soil get more nutrients and it gets fertilized.

That means the plants have more nutrients. That is why I think segmented worms are

very important to our ecosystem.

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Vocabulary Words

Aerate: to supply with air

Setae: bristlelike structures on the outside of each body segment that helps segmented worms move.

Crop: digestive system sac in which earthworms store ingested soil.

Gizzard: muscular digestive system structure in which earthworms grind soil and organic matter.

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References

Eldredge,N. 2008. Department of invertebrates. American Museum of Natural History.http://www.amnh.org/exhibitions/hall_tour/spectrum/27.html

Earthworm. 2008. From Wikipedia, the free encyclopedia. For the LPG album, see The Earthworm (album).[Online]

http://en.wikipedia.org/wiki/Earthworm#Reproduction

Glencoe/McGrawHill. 2008. Ch.13 Mollusk, Worms, Arthropods, Equinoderms. Section 2. Segmented worms. Printed in USA

Mitchell, A. 2008. All About Anatomy of a Worm. Published by head worm, [Online]<a href="http://www.allaboutworms.com" target=_blank>Check out the worms at All About Worms!</a>

Science encyclopedia vol.5. 2008. [online]

<a href="http://science.jrank.org/pages/6062/Segmented-Worms.html">Segmented Worms</a>

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Segmented Worms

Graphics

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SegmentationAllows movement with maximum protection.

2. Each segment contains repetition of excretory and movement organs.

3. Each is separated from others by a septum.

4. Segmentation provides an evolutionary framework to build upon.

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Segmented Worms Body

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Segmented Worms

Reproductive, nerve, circulatory and digestive systems

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Earthworm Digestion and Excretion

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Earthworm Circulatory System

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Earthworms Nerve Response

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Earthworms Reproduction