Segmented Worms - Project
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Transcript of Segmented Worms - Project
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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