23.4 Flatworms, Mollusks, and Annelids
KEY CONCEPT
Flatworms, mollusks, and annelids belong to closely
related phyla.
23.4 Flatworms, Mollusks, and Annelids
Flatworms are simple bilateral animals.
• they have a solid body and incomplete or absent gut
• there are three classes of flatworms:
head
pharynx
mouth
sucker
gut cavity
eyespot
reproductive
system
23.4 Flatworms, Mollusks, and Annelids
The first class is planaria
~ planarians can be terrestrial or aquatic
land-dwelling
planaria
can be found in very humid
environments
23.4 Flatworms, Mollusks, and Annelids
Land planaria feeds on earthworm
Image courtesy of Dr. Paul Choate, University of Florida
23.4 Flatworms, Mollusks, and Annelids
freshwater
planaria
23.4 Flatworms, Mollusks, and Annelids
marine
planaria
23.4 Flatworms, Mollusks, and Annelids
23.4 Flatworms, Mollusks, and Annelids
The second class are flukes
23.4 Flatworms, Mollusks, and Annelids
And the third
are tapeworms
23.4 Flatworms, Mollusks, and Annelids
Phylum Platyhelminthes
• Examples/Groups
planaria, flukes, tapeworms
• Characteristics:
* most live by stealing nutrients
from a host (are parasitic)
*
food is pumped/sucked into the
body through the pharynx
23.4 Flatworms, Mollusks, and Annelids
* respond to their environment:
ganglia
- uses ganglia (nerve cells) that
control the nervous system – is
like a brain
- uses eyespots to sense light
- uses sensory pits to sense
food
eyespots
23.4 Flatworms, Mollusks, and Annelids
* respiration and circulation:
- flatworm is so thin that
oxygen and nutrients are
transported into the body by
absorbing it
simply
through the skin
from a higher concentration to
a lower concentration. This is
known as diffusion.
23.4 Flatworms, Mollusks, and Annelids
Reproduction:
* Asexually by fission = organisms splits in half
to make 2 organisms
23.4 Flatworms, Mollusks, and Annelids
* Sexually by internal
fertilization
- are hermaphrodites =
contains both male and
female reproductive
organs
23.4 Flatworms, Mollusks, and Annelids
6. Fluke is
ingested by
animals/humans;
1. Human/animal
waste in water
contains fluke eggs
2. Eggs hatch
into larva
5. Fluke leaves
shell & attaches
to grass
4. Larva grows
within shell
3. Larva seeks
snail in the
water
23.4 Flatworms, Mollusks, and Annelids
6. Fluke is ingested
by animals/humans;
can burrow into
human skin (walking
in contaminated
water); can be
ingested by eating
uncooked snails