Phylum Platyhelminthes
The Flatworms
Phylum Platyhelminthes
Examples include:
Planaria
Tapeworms
Flukes
Polyclad flatworms
Characteristics
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Bilateral symmetry
Flattened bodies
12,000+ species
1 mm to 10 m
Most aquatic or
parasitic
• External suckers or
hooks
More Characteristics
• No coelom
• Digestive tube with
mouth, anus, and
intestine.
• Food in through
mouth, undigested
food leaves through
pharynx
Muscles are both longitudinal
and circular
Classification
Phylum Platyhelminthes
The Flatworms
Class Turbellaria
Free living worms
Class Trematoda
Parasitic flukes
Class Monogenea
Parasitic flukes
usually on fish
Class Cestoda
Tapeworms
Class Turbellaria
• Planaria
• Polyclad flatworms
(marine)
• Creeping motion
achieved through
muscles and cilia
• Only class containing
free living worms
Class Trematoda
• All parasitic flukes
• Infect vertebrates,
including humans
• Leaflike form
• Hooks or suckers
• Liver fluke, blood
fluke, lung flukes,
swimmer’s itch
Class Monogenea
• Parasitic flukes,
primarily on gills or
external features of
fish
• Direct life cycle, with
a single host
Class Cestoda
• Tapeworms
• Internal parasites of
vertebrates, including
humans
• Holdfast called scolex
• 1000+ species
• Life cycle requires
two hosts