INVERTEBRATE DIVERSITY SECTION (Biol.201), Spr 2000

Dr. Kathy S. Williams (email kwilliams@sunstroke.sdsu.edu)

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Bilateral symmetry & getting a head: Flatworms

Bilateria: Most animals exhibit bilateral symmetry and are triploblastic (591, 592) * FIG. 32.4 Symmetry Most of the diversity of animals is found in 2 big lineages of Bilateria (604-606) * FIG. 32.3 Animal Clade

These lineages possess a true COELOM (What’s a COELOM?)
        (593-594, * FIG. 32.6, 943-944)
 

• Deuterostomes

• Protostomes


Bilateria can have a cavity for organs between gut & body wall, but many
    don’t have a true coelom

* FIG. 32.5 Body plans of bilateria

• acoelomate animals (no body cavity at all)

• pseudocoelomate animals (false coelom)
 

Platyhelmenthes are examples of acoelomate Bilateria

They are bilateral, triploblastic animals without coelomic body cavities

* FIG. 33.9 Planarian Think:What is the embryonic origin of a) the epidermis, b) cells surounding the
        gastrovascular cavity, and c) cells and tissues between those 2 layers?
 

Flatworms were the first animals to invade many different habitats
    and evolved ways to solve problems associated with life on land
    & in fresh water.

 
• relationship between flattened body plan & respiration (826-827)

• maintaining body shape on land (1011-1012)

• possess simple sensory organs (photoreceptors 996, nervous system 976-977,
       *FIG. 48.13 ladderlike nerves)


Think: How do Platyhelmenthes reproduce?

• maintaining water balance (875-878); simple excretory organs
    (protonephridia; 879-880, * FIG. 44.15 protonephridia)

Think: In what way did the development of a simple excretory
        system allow Turbellaria to invade fresh water and terrestrial
        environments?

Diversity within Platyhelmenthes (604-606)

 
• Turbellaria are free-living flatworms with special features ª adaptations for life in fresh water

ª greater activity of flatworms is aided by specialized tissues

 • But most of the flatworm species are parasites, including ...  
ª tapeworms (Cestoda) - internal parasites of animals * FIG. 33.11 Tapeworm ª flukes (Monogenea) - external parasites, usually of fish

ª flukes (Trematoda) - internal parasites of animals

* FIG. 33.10 Schistosoma life cycle Adaptations for life as a parasite
  • feeding & attachment

• reproduction & life cycles; HERMAPHRODISM (914-915, 917)

• excretion

         CLICK ON FIGURE TO GET LARGER VIEW


Consider the effects of parasites on world health and agriculture.

In class writing (3/17)
Briefly explain 1 feature that distinguishes Cnidaria  from Platyhelmenthes.  (3 pts: using 3/2/1 pt rubric)
For Review
 Note that you may be quizzed or examined on items not covered on this list. In general, consider the exercises as "guides" to specific topics considered important.  For example, you might try to construct your own questions about a topic, then answer them, to deepen your understanding.  You will need to know more than just the following to get do well in this course … consider these exercises as a study guide.  Contact Dr. Williams or your TA for help. By now you should have read and taken notes on (at least!):
  overview of anim phylogeny & diversity 589-595

Parazoa 599-601

Radiata 601-603

Acoelomates 604-606

Pseudocoelomates 606-607
 
 

 By now you should be able to (in less than half a page):
  Explain major differences among Porifera, Cnideria, and Platyhelminthes.

Distinguish between radial & bilateral body symmetry.

Discuss advantages of radial symmetry for sessile (attached) animals and
bilateral symmetry for motile animals.

List characteristics of Platyhelmenthes that distinguish them from the other
animal phyla.

Explain major adaptations to a parasitic lifestyle.

Describe the generalized life cycle of a parasitic flatworm (like a trematode)
and give an example of one fluke that parasitizes humans. * FIG. 33.10

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