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					Worms
         Flatworms
                   Flatworms are invertebrate.

                   It has a head, or anterior end,
                   and tail, or posterior end.
                   Like most animals, flatworms
                   are bilaterally symmetrical.




Examples: Tape worms & blood flukes.
         Bilateral Symmetry
 Body plan in which an animal can be divided
  into two equal sides.
                 Structure
 Gastrovascular cavity – gut with a single
  opening.

 Cephalization – concentration of sensory
  organs towards the anterior end.
         Digestion & Excretion
 Pharynx – takes up
  food.

 Enzymes excreted to
  break down material.

 Nutrients diffuse to
  other parts of the body.
 Flame cells – collect
  excess water.

 Water travels through
  network of tubules
  and is eliminated
  through pores on the
  body surface.
      Roundworms (Nematodes)
 Examples: hookworms,
  pinworms

 Pseudocoelomates:
  hollow fluid filled cavity
  - lined by mesoderm on
  the outside and
  endoderm on the side.
   The body of a roundworm
It has a complete digestive tract:
    Two openings: mouth and an anus at opposite ends.
    Food only travels one way.
        Segmented Worms:
            Annelids

 Their bodies are
  divided in segments,
  or sections.

 Example: Earth Worm,
  leeches
             Characteristics
 Symmetry – Bilateral

 A segmented coelom – allows different parts
  of the body to move independently.

 Setae – external bristles.
                     Coelom
 The body cavity of annelids is called coelom.
 A coelom is a fluid-filled cavity completely lined by
  tissue that originated from mesoderm tissue.
       Structure and Movement

 Anchor middle section
  using setae.

 Contraction of the
  longitudinal muscles
  causes the worm to
  move forward.
           Feeding and Digestion
 Pharanx – muscular structure that sucks in soil.

 Esophogus – food passes through here.

 Crop – temporary storage

 Gizzard – grinds soil, breaking
  up organic matter.

 Intestine – absorbs organic
  compounds and nutrients.

 Anus – expels waste.
                  Circulation
 O2, CO2, nutrients &
  wastes transported
  through blood vessels.

 Aortic arches connect
  the dorsal and ventral
  blood vessels.

 Contraction of vessels
  and arches circulates
  the blood.
                Respiration
 Obtaining Oxygen:
  – Diffusion through skin


 Nephridia:
  – Tubes that eliminate excess water and wastes.
                Reproduction
 Hermaphrodites

 Setae and mucus secreted by the clitellum hold
  the worms together.

 Secrete sperm into the
  mucus and it is stored
  in the seminal receptacle.
              Reproduction
 After they separate the clitellum secretes a
  tube made of mucus and chitin.

 This tube picks up the worm’s eggs and
  sperm  fertilization.

				
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posted:3/11/2012
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