Biology 11 –
Kingdom Animalia
Study of the Primitive Worms
Phylum Platyhelminthes: Flatworms
Phylum Nematoda: Roundworms
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Phylum Platyhelminthes – the Flatworms
The Planarians
The Tapeworms
The Flukes
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Importance of the Flatworms to Evolution

Bilateral body plan – left side mirror image of right

Cephalization – development of the head


sense organs and nerves concentrated in head region
Centralization of nervous system:

Nerve cord accompanies cephalization and bilateral symmetry.

Advanced muscle tissue present;

Primitive excretory system

allows removal of metabolic wastes
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Phylum Platyhelminthes Characteristics

Bilateral symmetry; anterior and
posterior ends.

Body flattened

Well developed Epidermis

No internal body cavity other than
digestive tube (acoelomate)


Parenchyma (connective tissue)
fills space between organs.
Incomplete digestive system

Still one opening

This critter eats and poops out of its
mouth – mmmm, pass the
popcorn
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Flatworm Nervous System and Excretory System
Characteristics

Nervous system with ganglia and longitudinal nerve cords and branches

Simple sense organs; eyespots in some.

Excretory system

Lack circulatory, respiratory, and skeletal systems.
Reproductive system complex;
 Well-developed gonads and accessory organs.


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Free-living (eg Planarians) have well developed digestive and nervous
systems to seek-out and process food
Parasitic Tapeworms – rely on host’s digestive system to process food,
which absorb. No need for advancement of nervous system – not
needed.
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Nervous System and Sense Organs

Have a Nerve-net.

Most have more complex system.
 Cerebral ganglion = primitive
brain coordinates impulses.
 “Ladder” system carries impulses
throughout body

Many sense organs present
 Eyespots
 Chemoreceptors, touch sensors
and rheoreceptors (sense
direction) also common
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Advantage of Being Flat

Surface area to volume
ratio is important for
organisms.
3mm


many substances enter
and leave through body
surface.
3mm
3mm
Volume = 3 x 3 x 3 = 27mm2
Area = 6(3 x 3) = 54mm3
Faster absorption and
release of wastes
9mm
3mm
1mm
Volume = 9 x 3 x 1 = 27mm2
Area = 2(9 x 1) + 2(3 x 1) + 2(3x9) = 78mm3
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Cross Section of a Flatworm
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Nutrition and Digestion

Typical digestive system includes a
mouth, a pharynx, and an intestine.

Parasitic Tapeworms and Flukes
lack a digestive system

Free living flatworms (Planarians) are
carnivorous; suck prey into pharynx
with mouth.

Undigested food goes out mouth.
Yes, folks, they eat and excrete out
the same hole 

Parasitic flatworms, such as the
Tapeworm absorb molecules from
host.
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Reproduction – in Free-living Flatworms
such as Planarians

May reproduce sexually or asexually

Asexual:
 Binary fission – split in two

Sexual:
 Both sexes present in same
flatworm (hermaphrodites).

Fertilization internal, eggs
produced

Embryos emerge as juveniles
resembling adults.
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Reproduction in theTapeworm!

Lack digestive system

Sucker and hooks on anterior
end for attachment

Neck produces new segments
 Called proglottids

Each proglottid contains male
and female gonads

Reproductive output high
 Many proglottids per worm
 Many eggs per proglottid
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Tapeworm - Life Cycle
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Flukes -- Life Cycle of a Liver Fluke
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The Coelom or Body Cavity Advances
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Another Look at the Coelom
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Roundworms
Phylum Nematoda
Non-segmented; have smooth body wall
Generally colorless, less than 5 cm in length,
occur almost everywhere
Parasitic roundworms Live anaerobically in every
type of animal and many plants
Have tube-within-a-tube body plan
Digestive tract is complete; has both mouth & anus
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Roundworm Ecological Roles




Carnivores that catch and eat algae, fungi, decaying
matter
Recyclers
Parasites of Plants – eg. The Golden Nematode attacks
potato crops, causing severe devastation
Parasites of animals -
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Ascaris – Parasitic Roundworm of Pigs and
Humans
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Unfortunately, they can Grow quite Big!
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Parasites: Your Pet's Enemies
Tiny parasites that pose a gigantic threat
Heart worms inside the dog's heart, can
grow to a length of 14".
What they do:
Restrict blood flow and cause organ damage.
Symptoms include coughing. labored
breathing, heart failure. Untreated, heart
worm disease can kill a dog. Death may
occur within 72 hours.
How they spread:
Transmitted by over 70 species of
mosquitoes. Virtually all dogs are at risk.
Defending against them: Once a month
prevention is recommended, contact your
local veterinarian for advice.
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Adult roundworms live in the dog's
small intestine.
What they do:
Cause diarrhea, vomiting, stunted growth,
rough coat, bloated belly.
How they spread:
Almost all puppies get roundworms from their
mothers. Dogs can also pick up roundworms
from the soil.
Defending against them: Once a month
prevention is recommended, contact your local
veterinarian for advice.
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Enlarged hook worm mouth
showing 'teeth'.
What they do:
Attach to the dog's intestinal lining, leaving
bleeding internal wounds. Cause blood loss,
anemia, and diarrhea. As few as 100 hook
worms can kill a puppy.
How they spread:
Eggs pass through the feces of an infected
dog into the soil where they are easily
swallowed or can penetrate through a dog's
feet.
Defending against them: Once a month
prevention is recommended, contact your
local veterinarian for advice.
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Symptoms:
Larvae digested
enter bloodstream
and burrow into
organs, causing
absolutely
horrendous pain
and in some cases
death.
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Filarial (threadlike worms) are nematodes that
may block the passage of Fluids in the Body

Disease: Elephantitis

The disease is caused by
parasitic worms, including
Wuchereria bancrofti, Brugia
malayi, and B. timori, all
transmitted by mosquitoes.
Lymphatic filariasis currently
affects 120 million people
worldwide, and 40 million

Blocks Lymphatic nodes
which drain fluid to and from
the blood.
Tropics, Africa and Asia

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