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What are Flatworms ?
Flatworms are the simplest forms of
the worm group. The scientific name is platyhelminthes from
Greek - platy: flat, helminth: worm. There are about 25,000
species of these worms. They are found in marine, freshwater and
damp environments.
They require a moist environment to survive as they do not have
a skin to prevent drying. Most flatworms are parasitic and live
inside animal or human bodies. They can be brilliantly colored
creatures that swim in the ocean to parasitic flatworms that
live inside the bodies of an estimated 200 million humans around
the world.
Anatomy
Flatworms are bilaterally symmetrical with a clearly defined
head and tail region. They are elongated, flattened worms and
consist of
• Centralized nervous system:
The nervous system consists of a network with a brain and nerve
cords. Group of cells called eyespots are present on the worm’s
body. An eyespot is a light-sensitive cell on the surface of an
animal's body. The cell only detects changes in light and dark
and cannot gather enough information to see an image. When the
eyespot is stimulated by light, the organism reacts by moving
out of the light. The head region of the flatworm also contains
other paired sense organs that are connected to the flatworm's
simple brain.
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• Three tissue layers:
Beneath the outer layer, there are two layers of muscle an
outer circular layer and an inner longitudinal layer. This
enables the organism to move in an undulating form. A saclike
digestive cavity with a single opening that serves as both mouth
and anus is present in certain types and is branched; in the
simpler forms it is absent. The flatworms have no body cavity,
no circulatory system and no hard skeleton.
• Reproductive System:
Flatworms are hermaphroditic i.e. each individual organism
produces both eggs and sperm. The worms are capable of sexual
and asexual reproduction. Flatworms are able to reproduce
asexually by binary fission in which the organism can become two
by pinching themselves apart and by regeneration in which the
organism produces an entire new worm from a piece that has been
cut off. |
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Types of
flatworms: There are three classes of flatworms
•Turbellaria
•Trematoda
•Cestoda
Class Turbellaria Flatworms
belonging to this class are non-parasitic, free-living, and
primarily carnivorous. They are characterized by a soft
epidermis that is ciliated, and helps in the movement of the
organism. Larger species glide along by muscular waves over
mucous beds secreted by special cells. They range in size from a
few millimeters to a half meter long. A lot of energy is used
for the production of mucus to lubricate and protect the surface
of the body and to help capture prey. Most are hermaphroditic.
The planarians are relatively large flatworms named for their
three-branched gut and have more sense organs and a more complex
brain than the other turbellarians. They are mostly found in
freshwater.
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Class trematoda These are
parasitic worms and also called flukes having a flat leaf-like
body. They have oral suckers, with hooks, with which they attach
to their host bodies. They have the same body form and digestive
cavity as the turbellarians. The entire interior is occupied by
the reproductive system and is capable of producing huge numbers
of offspring. Adult trematodes can release up to 20,000 eggs per
day. Trematodes have a complex life cycle involving several
stages of larvae and many hosts. Many species, such as the liver
fluke Clonorchis sinensis and the blood fluke (Schistosoma),
cause serious diseases in humans.
Class cestoda These
flatworms are mainly parasitic and have long, flat, ribbon-like
bodies. They are commonly known as tapeworms. They have hooked
suckers on their head to attach to the host body. They do not
have a mouth or digestive system and food is absorbed directly
through the outer layer. Tapeworms can reach a length of more
than 30 meters making them amongst the longest known
invertebrates. |
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Article
Contributed By: Jaya Suresh
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