Download CH 27-1 FOLDABLE CONTENT FOR FOLDABLES

27-1 Foldable Content “Inside”
a long slender body allows the worm to move
about more rapidly than a radially symmetrical
body.
Worms can move forward in a single
direction rather than remaining stationary or
drifting in currents.
ALSO, the mouth, sense organs & brain
(if there is one!) are usually located at the
anterior end, or head of the body. This allows
the worm to locate food & respond to stimuli as
they move.
Flatworms & Roundworms…(Flatworms
are the simplest of the two)
Most flatworms are no more than a few
millimeters thick. They are soft, flattened worms
that have tissues & internal organ systems. They
are the simplest animals to have three embryonic
germ layers, bilateral symmetry, & cephalization.
Most have enough cephalization to have what is
called a head.
An animal lacking a coelom, or body cavity.
A fluid-filled body cavity lined with mesoderm.
some essential body functions such as
respiration, excretion, & circulation. Other
processes are carried out in different ways in
different species. Free-living flatworms have
organs systems for digestion, excretion (in some),
response, & reproduction.
Tapeworms and Blood Flukes are examples of
parasitic flatworms
Parasitic flatworms do not have a digestive tract
because they rely on their host’s digestive
system. Free-living flatworms have a single
opening digestive tract that has a PHARYNX
(muscular tube) near the mouth that extends out
and pumps food into the digestive cavity;
In free-living flatworms a head encloses several
groups of nerve cells that control the nervous
system. The groups of nerve cells are referred to
as Ganglia (Ganglion: singular);
A group of cells that look like eyes near the
anterior end of the body, but are actually
groups of cells that detect changed in light.
Most free-living flatworms have some type of
specialized cells that detect external stimuli,
such as chemicals in food, or the direction in
which water is flowing.
Free-living flatworms move either by the used
of cilia on their epidermal cells to help them
glide through water or over the bottom of a
stream or pond…OR by the use of muscle
cells that allow them to twist and turn in
response to stimuli.
Most free-living flatworms are hemaphrodites
that reproduce sexually. (HERMAPHRODITE= an
individual that has both male & female
reproductive organs. They generally DO NOT
fertilize their own eggs). Asexual reproduction is
also common in free-living flatworms. It takes
place by FISSION, in which an organism splits in
two & each half grows new parts to become a
complete organism. *Parasitic flatworms have
complex life cycles that involve sexual and
asexual reproduction.