On earth, some of the unicellular creatures evolved into multicellular forms. This took many millions of years.  The life forms that we studied in Unit Five could produce their own food, and are called homeotrophs, but the organisms that we are studying today had to capture organic molecules that they could break down into energy.  These are heterotrophs, some of which we call animals on earth.  

      The earliest animals began to develop differentiated tissues.   Some of the fossils look as if the animals had been flat, perhaps like the algae in which all cells have direct access to the water.  Some, like sponges, did not show much cell differentiation, and became communities of very similar cells.  As these early and primitive animals continued to evolve their cells began to differentiate more and more from one another as they became cooperating members of a single organism.

As animals (heterotrophs) cannot make their own food, multicellular animals, even primitive ones, had to find ways to capture nourishing chemicals. In the sea, some of the animals were mobile, and discovered the advantages of moving quickly or hiding well. Others, like sea anemonies, stayed in one place, like plants, and strained digestible material from the water flowing by.

• Introduction to Session Six --Body Plans and Environments 
• Helpful Web Sites
• Science Notes
  • Design Your Water Animal for Evolution
  • Introduction to Biomes
  • Introduction to the Animal Phyla

    • Porifera -- The Sponges

    • Cnidaria -- Jelly Fish, Sea Anemonies and Corals

    • Echinodermata -- Sea Stars and Sea Urchins

    • Mollusca -- Clams, Snails and Octopi

    • Arthropoda subphylum Crustacea -- Crabs and Shrimps

    • Chorodata -- Animals with Backbones

• Invertebrate or Vertebrate?
• Hunt or Hide?
• Strategies: Exoskeletons
•     No Skeletons: worms, Jellyfish
•     Clams and Other Crustraceans Starfish
•     Endoskeletons: Skeletons Inside fish
•     Fishes
• Gills: Oxygen, Metabolism, and Temperature
• Life in the Darkness
• How Animals Travel
• Animals and Plants in the Water

• Check Chapter 6 on the WorkSheet Master Page to Get Ideas About Making Your Animals Evolve
• What You Should Know: Study Questions for Test Preparation
• Go on to Lesson 7
• Return to Lesson Index Page.

• discuss how your animals came into being, how they move, and what they eat . Sketch the developmental phases of your aquatic animals
• draw a diagram to show how the animals are related to each other
• write descriptions of the animals, telling how they eat, move, reproduce
• each person will design his or her own aquatic animals.

Homework: Bring to class next session:

• written descriptions (on a web page) of how your animals evolved.
• written descriptions (on a web page) of the individual kinds of animals.
• computer drawn or scanned drawings of your creatures evolving in stages
• can you diagram the internal structure of your creatures?
• a computer drawn diagram of how the animals are related.