KEY CONCEPT Sponges and cnidarians are the simplest animals. - PowerPoint PPT Presentation

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KEY CONCEPT Sponges and cnidarians are the simplest animals.

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Title: PowerPoint Presentation Author: McDougal Littell Last modified by: HMCo Created Date: 9/14/2006 4:17:10 PM Document presentation format: On-screen Show – PowerPoint PPT presentation

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Title: KEY CONCEPT Sponges and cnidarians are the simplest animals.


1
KEY CONCEPT Sponges and cnidarians are the
simplest animals.
2
Sponges have specialized cells but no tissues.
  • Sponges are the most primitive animals on Earth.
  • 570 million-year-old fossils
  • closely related to group of protists
  • Sponges share common characteristics.
  • sessile
  • reproduce both sexually and asexually
  • filter feeders

3
  • Sponges have several types of specialized cells.
  • pinacocytes
  • choanocytes
  • amoebocytes

4
Cnidarians are the oldest existing animals that
have specialized tissues.
  • Cnidarians have two body forms.
  • polyps

In the polyp form of a coral, the tentacles and
mouth face upward.
5
  • medusas

In the medusa form of a jellyfish, the tentacles
and mouth face downward.
6
  • Cnidarians are made up of two tissue layers
    separated by mesoglea.
  • The outer tissue layer has three cell types.
  • contracting cells
  • nerve cells
  • cnidocytes (which contain nematocysts)

7
  • The four major cnidarian classes are defined by
    their dominant body form.
  • Anthozoans such as sea anemones have a dominant
    polyp stage.

8
  • The four major cnidarian classes are defined by
    their dominant body form.
  • Hydrozoans such as hydra alternate between forms.

9
  • The four major cnidarian classes are defined by
    their dominant body form.
  • Scyphozoans are jellyfish with a dominant medusa
    form.
  • Anthozoans such as sea anemones have a dominant
    polyp stage.
  • Hydrozoans such as hydra alternate between forms.
  • Scyphozoans are jellyfish with a dominant medusa
    form.
  • Cubozoans such as sea wasps have a dominant
    medusa form.
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