Body Structure
•
Flatworms are acoelomates with
bilateral symmetry.
•
Belong to phylum Platyhelminthes
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Thin, flat, ribbon-like bodies
•
Definite head region and body
organs
•
Most flatworms are parasitic, but
some are free-living
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Flatworms
Body Structure
Feeding and digestion
•
Free-living flatworms feed on dead or slow-moving organisms.
•
Extend a tubelike pharynx out of their mouth which releases digestive
enzymes
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Flatworms
Body Structure
Feeding and digestion
•
Parasitic flatworms have modified feeding structures called hooks and
suckers, which enable them to stay attached to their hosts.
•
Some have reduced digestive systems, others lack digestive systems and
gain nutrients through direct absorption from the host’s body.
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Flatworms
Body Structure
Respiration, circulation, and excretion
•
Flatworms do not have circulatory or
respiratory organs.
•
Cells can use diffusion to move dissolved
oxygen and nutrients
•
Flatworms do have an excretory system
that consists of a series of small tubes.
•
Flame cells lined with cilia sweep water
and excretory substances into tubules
•
Also excrete through their mouths
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Flatworms
Body Structure
Response to stimuli
•
Most flatworms have a nervous system consisting of two nerve cords with
connecting nerve tissue.
•
Flatworms have several anterior ganglion at the end of the nerve cord,
groups of nerve cell bodies that coordinate incoming and outgoing nerve
signals.
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Flatworms
Body Structure
Movement
•
Move by contracting muscles in the body wall
•
Glide by using cilia located on their undersides
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Flatworms
Body Structure
Reproduction
•
Flatworms are hermaphrodites.
•
Two different flatworms exchange sperm, and the eggs are fertilized
internally.
•
Free-living flatworms can reproduce asexually by regeneration, where lost
body parts can regrow whole organisms.
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Flatworms
Diversity of Flatworms
Turbellarians
•
Class Turbellaria consists of free-swimming flatworms
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Have eyespots, can detect presence/absence of light
•
Have chemical detecting cells
Trematodes
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Class Trematoda consists of parasitic flukes
•
Often require two hosts
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Flatworms
Diversity of Flatworms
Cestodes
•
Class Cestoda contains all tapeworms
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Anterior end composed of a scolex, a knob-shaped structure with hooks
and suckers for attaching to the intestine of a host
•
Body is composed of individual sections called proglottids, each of which
contains muscles, nerve cells, flame cells, and reproductive organs.
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Flatworms