Pseudocoelomate
Animals, Chapter 9,
Zoology
Phylum Rotifera
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Pronounced ro-tif' e-ra
Name means rota – wheel fero – to bear,
the wheel bearing animals.
The name comes from their ciliated crown
called a corona. When the corona beats,
it has the appearance of a rotating wheel.
Rotifers are microscopic or near
microscopic. They range in size from 40
micrometers to 3 mm but average
between 0.1 mm to 0.5 mm
Rotifers
Rotifer Ecology
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Rotifers are cosmopolitan (found
globally all over the world).
Most rotifers live on the bottom of
freshwater lakes or ponds, however a few
are marine and some are terrestrial.
Most rotifers eat plankton.
Some rotifers are parasitic.
Some rotifers are epizoic (live on the
surface of other animals).
Rotifer Anatomy
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Rotifers have a head, trunk, and foot.
The corona leads to the mouth.
The mouth leads to a muscular pharynx
called a mastax.
Their telescoping foot can attach to
substrates by secreting a sticky substance
that is produced by pedal glands and
secreted out their toes.
The digestive and excretory system of a
rotifer has a bladder and cloaca.
Rotifer Anatomy
Phylum Acanthocephala
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Pronounced (a-kan'tho-sef'a-la)
Name means acantho – spine or thorn,
cephala – head.
Often called spiny-headed worms.
Acanthocephalans get their name from a
distinct cylindrical proboscis that can be
protruded and bears many rows of spines
which attach to the intestinal wall of an
animal host.
All acanthocephalans are endoparasitic.
Most parasitize fish, birds, and mammals.
Phylum Acanthocephala
Phylum Nematoda (Roundworms)
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Name (nematos) means a thread
One of the most abundant types of worms in the
world. 12,000 species named, estimated 500,000
species worldwide yet to be discovered.
They live in a wide variety of habitats from the ocean,
freshwater lakes and streams, soil, from the poles to
the equator.
Good topsoil may contain billions of nematodes per
acre of soil.
They parasitize almost every type of plant and animal
in the world.
Most average about 5 cm (2 inches) in length.
However, they range in size from being microscopic to
some almost 1 meter (3 feet) in length.
Nematode Anatomy and
Locomotion
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Nematodes move by using the pressure
generated by fluid in their pseudocoelom.
This fluid-filled chamber that provides
structure and locomotion is called a
hydrostatic skeleton.
Hydrostatic skeletons work by transferring
the force of muscular contractions to a noncompressible fluid (hydraulic fluid pressure).
The pressure is contained by a thick cuticle
made of collagen.
Nematodes Hydrostatic
Skeleton
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In some animals like earthworms, circular
muscles and longitudinal muscles work
together to expand and contract.
Circular muscles are absent in nematodes.
Longitudinal muscles work antagonistically
against the outer cuticle like a spring.
When the longitudinal muscles contract, the
cuticle is stretched, when the longitudinal
muscles relax, the cuticle relaxes and causes
the body cavity to return to its original shape.
This causes nematodes to move erratically.
Nematode Pseudocoelom and
Longitudinal Muscles
Nematode Digestive System
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The digestive system of nematodes is
complete but simple and consists of a mouth,
pharynx, intestine, rectum and anus.
Nematode Nervous System
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The Nematode nervous system consists of a
ring of nerve tissue and ganglia at the anterior
end of the body that connects to two nerve
cords that run the length of the body.
Nematode Reproduction
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Most nematodes are dioecious (males
and females are separate sexes).
They exhibit sexual dimorphism and
males are usually smaller than females.
Fertilization is internal and eggs
(embryos) are stored in the uterus.
Eggs deposited by female, embryo
develops, juvenile hatches from egg.
There are four juvenile stages, each
juvenile worm is separated by a molt or
shedding of the cuticle.
Nematode Reproduction
Nematode Parasites
Ascaris lumbricoides
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Common name intestinal human roundworm.
One of the most common worms in humans.
Up to 25% of the southeastern US is infected
and over 1 billion people in the world.
Approx. 20% of the world's population.
Females can grow up to 30 cm long (1 foot).
Females produce up to 200,000 eggs a day.
Adults live in the small intestine and juveniles
leave the host's body in the feces.
Ascaris lumbricoides
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People become infected with intestinal worms
when uncooked vegetables are eaten or when
children put fingers or toys in their mouths.
Worm eggs are extremely resistant to harsh
conditions other than direct sunlight and high
temperatures. They can survive in soil for
months and sometimes even years.
When eggs are consumed they hatch in the
host's intestine, and penetrate the intestinal
wall to reach the hosts bloodstream.
Ascaris lumbricoides
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After reaching the host's bloodstream the
juvenile worms make their way to the lungs.
Once worms reach the lungs, the host can
develop a serious case of pneumonia.
After the juvenile worms are coughed up,
they are swallowed into the digestive tract
and make their way back to the intestine
where they become sexually mature adults.
Large numbers of adults can cause intestinal
blockage and severe abdominal pains.
Ascaris lumbricoides
Hookworms
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Hookworms get their name from their
anterior end which curves like a hook.
They burrow their hook mouths into the
intestines of humans and suck blood.
Can cause anemia in people and can
delay mental and physical growth in
children and cause a loss of energy.
Life cycle and transmission is similar to
ascarid (intestinal roundworms) worms.
Hookworms
Trichinella spiralis
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Responsible for potentially fatal
disease called trichinosis.
Females produce live young.
Juveniles penetrate skeletal muscles
where they burrow and develop into
large cysts called nurse cells.
If meat from an animal containing the
cysts is ingested, the juvenile worms
are liberated into the intestine where
they mature.
Trichinella spiralis
Pinworms
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Cause very little disease but are the most
common worm parasite in the United States.
Estimated 30% of children and 16% of adults
have pinworms in the United States.
Adults live in the large intestine.
Females migrate to the anal region of a human
host at night to lay eggs.
Scratching contaminates hands and bedsheets.
Eggs can then be transmitted and swallowed.
Contamination can be tested by the “scotch
tape method”.
Filarial Worms
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About 8 species infect humans
About 250 million people infected
worldwide, mostly in tropical countries.
Causes inflammation and obstruction of
the lymphatic system.
Mosquitos can carry the disease and
extreme manifestations can cause
elephantiasis.
Elephantiasis is a condition caused by
swelling of certain parts of the body such
as the legs, arms, and genitals.
Filarial Worms
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The most common form of filarial worm in
the US is the dog heartworm.
Carried and transmitted by mosquitos.
Can also infect cats, ferrets, sea lions and
occasionally humans.