WORMS
Biology 111
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:

 ectoderm,
mesoderm and endoderm
Worm Phyla!
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We will be looking at the 3 most important
worm phyla:
 Phylum
Platyhelminthes – flatworms
 Phylum
Nematoda - round worms
 Phylum
Annelida - segmented worms
Phylum Platyhelminthes (Flatworms)

General Characteristics:
 Types:
 Free-living
(more complex)
 Parasitic (simpler in structure)
 Very
flat, thin, often elongated body with a head
 Bilateral Symmetry
 Most primitive organisms to show cephalization
 Cephalization
is the concentration of sense organs and
nerve cells at the front of an animal’s body
 Sensory
organs in the anterior region (light/smell):
they can detect food and move toward it.
 Have a brain, nerve cells (control center)
Phylum Platyhelminthes (Flatworms)
Characteristics cont’d…

Acoelomates meaning they
have no coelom,
A
coelom is a fluid filled body
cavity
 Only
possesses a digestive
cavity

Single opening with which
both food and waste pass
through
Phylum Platyhelminthes (Flatworms)

Main Classes:
 Class
Turbellaria
 Planaria
 Class
Trematoda
 Flukes
 Class
Cestoda
 Tapeworms

Within the 3 classes, there are approx.
10,000 species
Class Turbelaria
(Free living flatworms)
Most are Free living – those that are NOT
parasites
 Complex but incomplete digestive system
 Most common are planarians (fresh or salt
water organisms) about 1 or 2 cm

Planaria (Class Turbellaria)
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


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Flame cells function like a kidney, removing excess
waste and releasing through ducts to the excretory
pores
Hermaphrodites – each individual produces male
and female gametes (sperm from one worm
fertilizes eggs of another worm)
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

If split lengthwise or crosswise, will regenerate 2
separate individuals
http://www.youtube.com/watch?v=w0QzS
YQGsnA
Class Trematoda (Flukes)

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Most common are 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 (Tapeworm)

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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)
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Proglottids – each segmentlike division of the body, each
contains male and female organs
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
http://www.youtube.com/watch?v=txSiApF
http://www.youtube.com/watch?
v=bb32g02IIs8
Phylum Nematoda (Roundworms)
Most are free-living; some are parasitic
 Most are harmless (except parasitic forms)
 Extremely common (10,000 species)
 Live in soil and water; polar to tropics

Small (less than a few mm in length)
 Round tubelike shape
 One way digestive tract (two openings); food enters
the mouth and waste is expelled from an anus
 Reproduce sexually, separate sexes for worms


Internal fertilization
Roundworms

Body cavity is partially lined with tissue derived
from the mesoderm and is called a
pseudocoelom, meaning, “false coelom.”

The body cavity that fills with fluid giving a round
shape. – much like air in a tire; fluid also circulates
material through the body
http://www.youtube.com/watch?v=GiHtUF
uGgSA&feature=related
http://www.youtube.com/watch?v=4p0kC1
Q3iOE
Parasitic Nematode - Hookworm
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)

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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