Platyhelminthes are a phylum of flatworms. They have an opening for ingestion and excretion but no anus. Most are parasitic and absorb nutrients directly from their hosts. They can reproduce asexually through fission. While some are free-living, most platyhelminthes are internal parasites of animals and humans that live in intestines and blood vessels.

1. Platyhelminthes
All photos by Flickr user: robgrowler
Transport Responses to Stimuli
Internally, flatworms have one digestive opening that Cestodes have limited censory ability since they are
branches to all parts of the body. Circulation occurs parasites and as adults they don’t have any.
through diffusion, which is when something goes Turbellarians have many organs that help them sense
from a higher concentration to a lower concentration. environmental stimuli. They use their hair and eyes
They excrete through flame cells, which are ciliated, to sense. Turbellarians and Monogeneas have paired
and induce currents sense organs in the head region including the eyes.
to push fluid through The organs are attached to their brain.
tubules. Externally,
the flatworms have Adaptation
bilateral symmetry,
and they can move Platyhelminthes always move from place to place
by using layers of They are almost everywhere. They often switch
muscles, or in some hosts. These organisms live inside of humans and
Photo by Flickr user: shane58 animals and mainly prefer fresh and marine waters.
species, by gliding
along a slime trail using cilia. The stomach is like a
sack. The food goes into the sack through the
mouth. Once food is taken into the body, the rest is
thrown back out of the mouth. (They have no anus).
Nutrition
Most platyhelminthes are parasitic. this exclues
Turbellarians. Monogeneas, Trematodas, and
Cestodas get their energy from the nutrients of their
hosts. When they attach to an organ they absorb the
nutrients from the area directly. Photo by Flickr user: Adam
Carvalho
Reproduction
A flatworm reproduces by splitting in two. When a Respiration
flatworm is split up it immediately forms a new
flatworm. Mainly all platyhelminthes have extracellular body
1 fluids that pass through their bodies to help distribute
gas, waste, and nutrients.

2. Platyhelminthes
November 3, 2009 Volume VII
another organism and feed directly from their blood
vessels. Non-Schistosomiasomes are also parasitic,
but they never directly target a host to feed off of,
they usually are ingested into cows or pigs and then
Regulation when we humans eat beef or pork, the
Platyhelminthes are moved into the body.
Platyhelminthes have
Photo by Flickr user: rebin1605 no circulatory system. Backround of Group
They regulate their
body temperature by keeping the extracellular fluids Almost all flatworms, or platyhelminthes, are
running through their body. parasitic. These organisms have one hole to
Type to enter text transport nutrients, and waste in and out. They have
General Structure no anus.
Turbellarians have cilia and flat bodies. Cestodas Other Organisms
and Trematodas have a thick cuticle that covers the Found in Group
body; they also have flat bodies. monogenea is a
flatworm that contains hooks, and a haptor. All of Other organisms
Platyhelminthes classes have three cell layers. found in the
Photo by Flickr user: Platyhelminthes are
Place in Food Chain wsdubstyle flukes, flatworms,
and tapeworms.
The Platyhelminthes are catagorized into two
groups, Schistosomiasomes and Non-
Schistosomiasomes. The Schistosomiasomes are
parasitic, they make their way into the body of
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3. Platyhelminthes
November 3, 2009 Volume VII
The “Oddball”
That Exists
Interesting Facts
Turbullarians are the
Platyhelminthes have a pharyngeal opening. This
“oddball” of the
opening allows them to bring food in and excrete
Photo by Flickr user: phylum. They are the
waste. The free living Platyhelminthes are very
piratemateo only class that doesn’t active and consume energy while they do it. They
contains parasites. are a paper thin structure and they do not have a
full digestive system, it only consists of a mouth.
Type of Symmetry
Flatworms
Platyhelminthes have bilateral symmetry. like to lurk in
dark places
Extinct or Endangered in waterways.
Flatworms
Lake Pedder Planarian is extinct. are found in
streams and
Their Importance to Our Lives shallow parts
Photo by Flickr user: Lou FCD of lakes. They
Flatworms may help humans become skinnier.
live in dark places on the surface of rocks
Ohter than this, Platyhelminthes are not a help to
and plants. The stomach is like a sack. The
humans, only a danger to the body.
food goes into the sack through the mouth.
Once the food is taken into the body, the
rest is thrown back out of the mouth.
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