Download 4. The embryo of flatworms has a third germ tissue

PHYLUM PLATYHELMINTHES
1. List three basic differences between cnidarians and the platyhelminthes and
describe the significance of each difference.
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Platyhelminthes have their tissues organized into organs and even have some
simple systems
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Exhibit Cephalization: Concentration of sensory organs and nervous tissue at the
anterior end of the body (head).
Cnidarians had a nerve net for conducting impulses, but the platyhelminthes have
centralized the nervous system into two longitudinal nerve cords. (faster
transmission of nerve impulses).
-Well-developed third tissue layer called the mesoderm between the ectoderm and
endoderm.
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The mesoderm has also provided for better muscle development and thus has resulted in
an animal that moves around more efficiently.
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bilateral symmetry
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-Possess an incomplete (blind) gut: single opening (mouth/anus) to the
gastrovascular cavity; use mouth to ingest food and use mouth to expel undigested
wastes
2. Platyhelminthes consist of flatworms. Why is this phylum name appropriate?
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They are no more than a few mm thick (length can reach 20 m)
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Dorsoventrally flattenned
3. Name the three classes of platyhelminthes and provide an example of each.
1. Class Turbellaria: -Free living
Example: Planaria
2.Class Trematoda:
Example: Flukes
3. Class Cestoda:
Example: Tapeworms
4. The embryo of flatworms has a third germ tissue layer (embryonic tissue) that
was not present in simpler animals like cnidarians. Identify this layer and explain
its significance in animal evolution.
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Mesoderm – was not present in earlier phyla
Mesoderm includes: reproductive, excretory, and muscular organs
Class Turbellaria
1. What are some general characteristics of members of this class?
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mostly free-living
primarily carnivorous
soft epidermis that is ciliated, at least on the ventral surface
incomplete gut
No suckers or hooks
Ciliated epidermis
2. Where are turbellarians found?
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Most in sea, some in lakes, streams and ponds
3. Describe the structure and function of flame cells.
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Freshwater Turbellarians have an organ system for salt/water regulation
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System is based on units called PROTONEPHRIDIA  each unit consists of branched
tubules that extend from a pore at the body surface to many cup shaped FLAME
CELLS in the body tissue
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Flame cells have a
tuft of cilia that
“flickers” within them
 excess fluid moves
into the cups and the
flickering moves it
down the tubule
system to the outside
4. What are the two means of location used by free-living flatworms like planarians.
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CILIA - The movement of the cilia propels the smaller forms.
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MUSCLE CELLS – Larger species glide along by muscular waves controlled by nervous
system (allows them to twist and turn)
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Have glands in the muscle layers below the skin (which connect to the surface by
pores) that secrete mucus
5. How do planaria respond to stimuli?
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A pair of ventral (along belly) nerve cords run the length of a nervous system
Connect to a pair of small brains or ganglia (a group of nerve cells) at the anterior
end
Show cephalization with a variety of sensory cells
Sensory cells are sensitive to touch, light (ocelli), and various chemicals
6. Describe sexual reproduction in planaria.
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Most are hermaphrodites and have an organ that functions as a penis and a
structure for storing sperm received during copulation
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Mating between two individuals results in reciprocal transfer of sperm
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Eggs that are laid in clusters hatch within a few weeks.
7. Unlike parasitic flatworms, free-living flatworms can reproduce asexually.
Explain how.
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Fragmentation
regeneration
Class Trematoda
1. What are some general characteristics of members of this class?
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Parasitic
Incomplete gut
Suckers
Outer Cuticle (tegument)
_ 2. Where are flukes typically found?
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In gut, liver, lungs, bladder or blood of mostly molluscs and vertebrates
3. Sketch and label an adult
fluke.
4. Flukes have complex
lifecycles involving multiple
hosts. What is the difference
between a primary and secondary host?
Adult parasite and sexual reproduction is in primary host whereas
development occurs in secondary host.
5. Blood flukes are very common in southeast Asia. Humans are the primary hosts of
blood flukes that belong to the genus Schistoma. Outline the lifecycle of a blood fluke.
(p.729 in text)
6. Why are blood flukes a greater concern in undeveloped countries?
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Because human wastes, which may carry eggs of flukes, are not disposed of as in
developed countries (fewer toilet facilities and no sewage treatment)
Feces often tossed in water bodies and used as fertilizer (eggs hatch in water and
become ciliated larvae)
7. What is schistosomiasis a n d w h a t are the short and long term effects of
schistosomiasis in the body.
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Short term – deterioration of liver, heart, spleen, bladder and kidneys cause person
to feel sick &weak
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Long-term- death due to flukes or b/c body cannot recover from other illnesses in its
weakened state
8. What is "swimmers itch"?
 Some flukes have fishes or water birds as their primary hosts so if
they burrow into human skin, they cannot live there b/c they are
not adapted as human parasites  instead cause itchiness
Class Cestoda
1. What are some general characteristics of members of this class?
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Parasitic
No gut
Suckers and hooks together form a scolex for attachment to host
Body consists of repeating sections called proglottids.
3. Describe the following body structures of a tapeworm:
scolex-
-head of tape worm that has suckers, hooks or both
-use it to attach to intestinal wall of host
proglottids -neck
region is constantly
dividing to form
units called
proglottids
-each one has
ovaries and testes
-proglottids of a
tapeworm can
transfer sperm
4. Outline the lifecycle of the beef tapeworm.