Characteristics and symmetry of Flat Worms
Radial vs. Bilateral Symmetry
Bilateral Symmetry: arrangement of body parts so
that there are left and right halves that are
mirror images of each other. .
Classes of Flat Worms.
Flatworms belong to the phylum Platyhelminthes
1. Turbellaria – Marine flatworms
Example: Planarian
Objectives: 1) 1) Describe the difference
between radial and bilateral symmetry. 2)
Draw an example of a planarian, tapeworm,
fluke, and roundworm. Label the pictures
accordingly. 3) Describe the roundworm life
cycle.
2.Cestoda – Tapeworms (parasitic)
Every segment (proglottid) contains both
male and female reproductive parts leading
to self-reproduction. Tapeworms attach to
the intestines by the hooks and suckers
located on the head.
3. Trematoda – Flukes (parasitic)
*** The danger posed by tapeworms and flukes is
the embryo stage of these parasitic worms.
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Roundworm Body Plan
Roundworms belong to phylum Nematoda
1) Cylindrical in shape.
2) Possess a fluid filled body cavity. This
cavity serves as a circulatory and
respiratory system
3) Muscles line up between the body
cavity and the skin.
Parasitic Round Worms
Some roundworms are parasitic towards plants or
animals.
The eggs/embryos of roundworm infect humans.
Example: Hookworms
1) Transmitted by contact with human waste.
2) Ingest a hookworm egg.
3) When reaching the intestine, the egg develops
into a larva.
4) Larva tunnels through the lungs where they cause
respiratory disease before going back to the
intestines to mate and make more worms.
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