Transcript Flatworms/Roundworms

Flatworms/Roundworms
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Phylum Platyhelminthes
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platy-flat, helminth-worm
three classes
1. Class Turbellaria
2. Class Cestoda
3. Class Trematoda
Bilateral symmetry
Non-segmented
no respiratory or circulatory systems: depend on diffusion to transport
nutrients.
Sense receptors and nerves found at the anterior end
Free living or parasitic
Found n rivers, lakes, and streams
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Class Turbellaria: Flatworms
a. free living
b. posterior end tapers, anterior end is spade-shaped
c. movement
1. swimming: muscle cells controlled by nervous system allow
to twist and turn
d. Feeding
1. scavengers
2. feed on protozoans
3. in the middle of their body, they have a small opening called
a mouth. A muscular tube called a pharynx, located behind
the mouth extends out of the mouth and sucks in the food.
The food is passed into the intestine. Nutrients are absorbed
by the intestinal wall through diffusion. Any waste or
undigested food are excreted through the pharynx and out
through the mouth.
4. Flame cells: located on the ends of the branches of the
intestines. Excess water are excreted through these cells.
e. Nervous control
1. Eyespots: located on the anterior end of the body. Sense
light
2. Ganglia: a cluster of nerve cells located on the anterior end of the
body. Extending from the ganglia are two cords running the length of
the body, Sense: touch, taste, and smell
f. Reproduction
1. Sexual: Hermaphrodites
a. no self-fertilization
b. fertilize each other at the same time: worms join,
one worm delivers sperm to another while receiving
sperm from its partner at the same time.
2. Asexual
a. Regeneration. They attach themselves and stretch
until they split in half. Each half regenerates.
g. Basic Structure:
1. gastrovascular cavity
3. mouth
5. Flame Cells
7. eyespots
9. posterior
2. pharynx
4. ganglia
6. Two nerve cords
8. anterior
10. Intestines
http://dragon.seowon.ac.kr/~bioedu/bio/ohp/t-162.jpg
Class Cestoda: Flatworms
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Parasitic flatworms: tapeworms
They have a head called a scolex suckers and hooks that allows them to attach themselves to
their host
Attach to intestinal walls
Food is absorbed through skin of parasite
Reproduce: proglotidds: rectangular body sections. They are reproductive units that are added
throughout the worms life. A proglottid can have up to 10,000 eggs.
There are more than 5,000 species of tapeworms known to science, and nearly every species
of vertebrate is liable to infection from at least one species of tapeworm .
Class Trematoda: Flatworms
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Largest class
Parasitic worms called flukes
Endoparasitic: live inside the host
Ectoparasitic: live outside the host
Have one or more suckers to attach to host. Use pharynx to suck body’s
fluids for food.
Reproduce: can have more than one host. EX: Shistosoma
1. Blood fluke responsible for shistosomiasis: found in tropics
2. People wade in infected water, and parasites bore through skin
and make their way to blood vessels. This causes bleeding and of
intestinal walls and liver damage.
3. Also includes a special species of a snail as part of their life cycle.
Roundworms
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Phylum Nematoda
Bilaterally Symmetry
Found Everywhere. Pets: wormed, soil, humans etc…
They have a body cavity that forms between the gut and the body
wall. Food passes into the mouth and is excreted through the anus.
Many nematodes are free living and play critical ecological roles as
decomposers and predators on microorganisms. But nematodes
also include parasitic species, a number of which affect humans
directly or indirectly through their domestic animals. These include
the common roundworms, which probably infest more than half the
world's humans; hookworms; trichina, the worms that cause
trichinosis and Ascaris worms; pinworms, another extremely
common parasite, even in the United States, which can be
transmitted from human to human by eggs floating in household
dust; and filarial worms, primarily tropical parasites that cause
diseases such as filariasis (elephantiasis) and onchocerciasis (river
blindness).
Trichinella
Ascaris
A cluster of nematodes,
the roundworm of dogs,
Toxocara canis.