Transcript c. flatworms and roundworms

Biology 11
Mrs. Trevelyan
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Platyhelminthes
1. PRESCRIBED LEARNING OUTCOMES
and VOCABULARY
2. VIDEOS:
None 
3. TEXTBOOK PGS
Section 26.3 pgs 706-710
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Overview…
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Examples of Members:
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Marine Flatworms are Beautiful!
Video: Marine Flatworm Swimming
http://www.youtube.com/watch?v=zCH37KI_R_E
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Three Classes of Flatworms
1. Turbellaria: Free-living flatworms, mostly predators, living in
water or moist environments
2. Trematoda: Flukes, all are parasitic and have complex life cycles
2. Cestoda: Tapeworms, all are parasitic and have complex life
cycles
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1. Unifying Characteristics
 Bilateral symmetry, no segmentation
 First to have 3 germ layers!
 Outer layer (epidermis) is soft and ciliated (has tiny hairs)
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or covered with a cuticle
Parasitic species have a mouth with an external sucker or
hook for attachment to a host
Digestive system is incomplete with only one opening
Muscle layer is well developed (can swim)
No skeleton, circulatory or respiratory systems
Hermaphroditic, use internal fertilization
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2. Structure
•Cephalisation has occurred (have a
head with a concentration of nerve
cells)
•Has 3 cell layers (ectoderm ,
mesoderm and endoderm) with
specialized cells and tissues
•Development of more complex
tissues and organs (e.g. Pharynx,
eyespot, muscle layers etc)
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2. Structure
•Some freshwater species have
primitive eyespots and can detect
the presence of light
E.g. Planarians
This eyespot is called an OCELLI and
is NOT a true eye
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3. Digestion
 One opening (“mouth” with a
gastrovascular cavity that is often highly
branched throughout the body)
• Free-living are carnivores or scavangerspharynx comes out of mouth and
“vacuums” up food, also “spits out” solid
waste
Video: Planarian eating
http://www.youtube.com/watch?v=w0QzSYQGsnA
•Parasitic flatworms anchor themselves to
their host and live off of host tissue/blood
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Digestion- some are PARASITIC
 Tapeworm in an intestine
 Most do not have a complete digestive system
because they absorb digested material directly
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4. Respiration/Excretion
RESPIRATION
 No Respiratory organs
 Exchange gases by diffusion (hence small, flat shape)
EXCRETION
• Solid wastes exit the body through the
“mouth”
• Gas wastes exit the body through diffusion
• Freshwater flatworms have FLAME CELLS
that excrete excess water from the body
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5. Nervous System
 More advanced than cnidarians
 Have cephalization and cerebral ganglia (brain-like
structure)
 Nerve cords are organized like a ladder (no netting)
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6. Reproduction
Flatworms are hermaphroditic (both male and female)
Can reproduce aseuxally or sexually
ASEXUAL REPRODUCTION:
Free-living freshwater flatworms can do this by:
a) Fission- organism splits in two
b) Regeneration- a single part can grow into a new worm
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6. Reproduction
SEXUAL REPRODUCTION
Freshwater free-living flatworms use internal fertizilation
Flatworms “join up” in pairs to reproduce sexually. One
delivers sperm, one receives sperm. Eggs are laid and
hatch in a few weeks
 Video: Marine Flatworms Penis Fencing:
http://www.youtube.com/watch?v=wn3xluIRh1Y
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6. Reproduction
Parasitic flatworms have a much more complex life cycle,
often with more than one host (e.g. infects snails and
humans)
See and know figure 26.18 on page 710
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7. Additional Interesting Facts
 flatworms sometimes growing to lengths of 40 feet
 Penis fencing- nuff said
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