Phylum Platyhelmenthes
Planarians, Flukes, & Tapeworms
•Simple acoeleomates
•Bilaterally
symmetrical
•Most flattened
"Dorsoventrally"
•Divided into 4
classes:
Class Turbellaria
•Most free-living and
non parasitic
•Include planarians
•Lack circulatory and
gas-exchange organs.
•Simple excretory
structures called flame
cells that maintain
osmotic balance.
•Is cephalized and has
eye-spots which are
sensitive to light
•Feeds through ventral
feeding tube called a
pharanx
•Can reproduce
sexually, or asexually
through regeneration
Planarian and assorted marine
flatworms…
Class Trematoda (Flukes)
• Similar in form to
turbillarians
• Many are parasitic.
Example of
parasitic fluke is
the asian liver
fluke
• Many have complex
life cycles
including multiple
hosts and
alternation of
generations.
Life Cycle of the Liver Fluke
Liver Flukes Cont’d…
Liver Fluke
Liver Fluke encysted in a liver
Class Cestoda (Tapeworms)
• Parasitic flatworms
• Can grow to enormous
lengths (up to 20m)
• Parasitize mostly
vertebrate hosts
• Attach head named scolex
to intestinal walls of
host, and abosrb host's
nutrients
• Following scolex is a
series of repeating
structural units called
proglottids
• Mature proglottids
containing thousands of
eggs are released with
the host's feces to
infect other organisms.
Tapeworms cont’d…