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KEY CONCEPT Sponges and cnidarians are the simplest animals .

KEY CONCEPT Sponges and cnidarians are the simplest animals. Sponges are the most primitive animals on Earth. 570 million-year-old fossils closely related to group of protists. Sponges have specialized cells but no tissues. Sponges share common characteristics.

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KEY CONCEPT Sponges and cnidarians are the simplest animals .

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  1. KEY CONCEPTSponges and cnidarians are the simplestanimals.

  2. Sponges are the mostprimitiveanimals on Earth. 570 million-year-old fossils closely related to group of protists Sponges have specialized cells but no tissues. • Sponges share common characteristics. • Sessile adult, motile larvae • reproduce both sexually and asexually • filter feeders • No tissues or symmetry

  3. Sponges have several types of specialized cells. spicule pore osculum pinacocyte amoebocyte choanocyte • Pinacocytes- outer layers • Choanocytes- filter feeding mechanism • amoebocytes -motile

  4. Cnidarians have twobodyforms. 1. polyps Cnidarians are the oldest existing animals that have specialized tissues. In the polyp form of a coral, the tentacles and mouthfaceupward.

  5. 2. medusas In the medusa form of a sea jelly, the tentacles and mouthfacedownward.

  6. gastrovascular cavity mouth mesoglea tentacle discharged nematocyst oral arms barbs coiled nematocyst • Cnidarians are made up of twotissuelayers (endoderm and ectoderm) separated by mesoglea. • The outer tissue layer has three cell types. • contracting cells • nerve cells • cnidocytes (which contain nematocysts to )

  7. Two anemones aggressively fight using their specialized sacs loaded with nematocysts that contain toxins. http://shapeoflife.org/video/cnidarians-anemones-fight

  8. The fourmajor cnidarian classes are defined by their dominantbodyform. • Anthozoans such as sea anemones have a dominantpolyp stage.

  9. Hydrozoans such as hydra alternate between forms.

  10. Scyphozoans are true jellyfish with a dominantmedusa form. • Cubozoans such as sea wasps have a dominantmedusa form.

  11. Sponges and Cnidarians Virtual Lab Link: http://www.glencoe.com/sites/common_assets/science/virtual_labs/LS13/LS13.html

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