Transcript WORMS - holyoke

WORMS
WORMS
Over 20,000 wormlike organisms
Classified into 6-8 different phylum
All have bilateral symmetry
Bodies have true tissues, organs and organ
systems
 Tissues derived from 3 germ layers: ecto, meso,
and endoderm
 We will be looking at the 3 most important worm
phyla: flatworms, round worms, and segmented
worms. (largest # of species and greatest
impact on humans)
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Phylum Platyhelminthes (Flatworms)
Characteristics:
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Divided into 3 classes: turbellaria (free living
flatworms; trematoda (flukes); and cestoda
(tapeworms)
Within the 3 classes approx. 10,000 species
Very flat, thin body
Have a head
Bilateral Symmetry
Sensory organs in the anterior region
(light/smell): they can detect food and move
toward it.
Flatworm characteristics cont…
Have a brain, nerve cells (control center)
 Most primitive organisms to show
cephalization
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Classes of Flatworms
#1: Class Turbelaria – (Free living
flatworms)
Free living – those that are NOT parasites
Most common are planarians (fresh or salt water
organisms) about 1 or 2 cm
 Have a “blind” digestive system: mouth is the only
entrance or exit.
 Have a nervous system
 Has two light-sensitive spots that resemble eyes on it’s
head (they sense light and dark)
 Take in excess water by osmosis; and remove excess
water by ciliated flame cells
 Hermaphrodites – each individual produces male and
female gametes (sperm from one worm fertilizes eggs of
another worm)
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Planarians cont…
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Most are carnivorous (eat protists/small animals)
which they trap in secretions from their mucous
glands.
They grasp its prey with its mouth and wrap
their body around the prey
The pharynx breaks food organisms into small
pieces and pushes them into the gut. Food
molecules are diffused from gut cells to the
other body cells.
Undigested food is expelled through the pharynx
and the mouth.
Ability to regenerate
Class Trematoda: Flukes
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Parasitic flatworms
Organs and organ systems similar to planarians
Outer layer has a tough, nonliving material
called a cuticle that protects it from digestive
enzymes of its host.
Have two suckerlike disks; one on the ventral
surface & one around mouth
Suckers attach the worm to the host (host’s
digestive tract) and it absorbs digested food
from the host’s intestine
Class Cestoda: Tapeworms
All cestodes (tapeworms) are parasitic flatworms
 Tapeworms are more specialized than flukes
 Body is divided into many sections or proglottids (and it
will continue to make more of these sections just behind
its head)
 Species vary in length and number of proglottids – some
have thousands
 No digestive system (they live in the intestine of a host
 Several human tapeworms are transmitted by infected
pork, beef, or wild game that hasn’t been cooked
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http://www.youtube.com/watch?v=txSiApFzaZE
Tapeworm
Phylum Nematoda: Roundworms
Round tubelike shape
Extremely common (10,000 species)
Small (less than a few mm in length)
Soil and water
Most are harmless (except parasitic forms)
One way digestive tract (two openings); food
enters the mouth and waste is expelled from an
anus
 Have a body cavity that fills with fluid giving a
round shape. – much like air in a tire; fluid also
circulates material through the body
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Parasitic Nematodes
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Hookworm is a common roundworm parasite of humans
Occurs where sanitation is poor and where human
wastes are used as fertilizer, or where people are
commonly barefoot
Human waste from an infected person contain
hookworm eggs. Eggs get in soil and develop into larval
worms. Larval worms contact skin and pierce through
and burrow in the body. Larvae is carried by the blood
to different body parts. Adult worms attach to the
intestine wall and feed on blood and tissue.(ex: sheep
liver fluke)
http
http://www.youtube.com/watch?v=GiHtUFuGgSA&feature=related
Hookworm
Hookworm Info.
Affects 1 billion people worldwide
 Commonly causes death in children
because it increases their susceptibility to
other diseases that could normally be
tolerated
 Very little chance of contracting it in the
US or Canada due to our advances in
sanitation and waste control
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