World Builders™
World Builders™
Session Six  -- Water Animals
Session Six --  Water Animals

Introduction to Water Animals
Introduction to Water Animals

Body Plans and Environments

It is time to think about your animals.
  • Where are they going to live?
  • What will they eat? Check out the plants that were created last week.
  • Who will try to eat them?
  • Remember that you will need to create an animal for each of the biomes that you worked with last week.

     If an animal is defined as an organism with a digestive tract, we can see that a primary drive for animals is finding food.  

     There are some basic roles in ecosystems.  A role plus the resources that support it are called a niche.  

The Deep Ocean

turtle     Ocean creatures are supported by water. Many of them can float freely, and so can use their energies for movement rather than just for holding their bodies up. There is great variety of body forms among water animals. Just look at some of the examples on these pages!

     Last week we considered two different possible environments, the open sea and the shallow water near the shore. In the open sea the plants are pelagic, (that means that they float at the surface), so many of the animals in the floating community will also be pelagic, hiding in tangles of sea weed and eating plants or each other. This pelagic community includes unicellular life forms, tiny crabs and snails, and fishes that are very small or very young. Although there is a lot of light out on the open ocean, nutrients are lost as bits of dead plants and animals drift downward. This community will not be as diverse as a community in shallow water, and many of its members will be small.

     Below the surface of the open ocean lie the depths. On earth there are specialized animals in the cold darkness of the deep ocean. There is not much to eat down there, just dead matter sinking down from the life forms in the sunlit zone. Organisms that eat this dead matter are called decomposers. They take the debris apart chemically so that the chemicals can be cycled through the biosphere again. However, circulation in the deep ocean is very slow, and the nutrients may not be returned to the surface for many hundreds of years. Some of the nutrients get buried in the sediment at the bottom of the ocean.

     Scientists have recently discovered that there are communities of animals and plants around active volcanic vents in the deep ocean. These plants and animals live in the dark, so photosynthesis, the energy-capturing process used by plants at the surface, could not work for them. Warm, chemically rich water, comes out of these vents, which may also release lava and gases. The plants use the chemicals and heat in a process called chemosynthesis, transforming the chemicals into food. These communities are models of small, fairly self-contained ecosystems. The life forms there can only survive close to the vents. The greater part of the cold, dark ocean depths are not hospitable to them.

Shallow Water sea anenome

Shallow waters offer animals many opportunities to find different ways to live.
  • They can crawl on the bottom.
  • They can hide in the mud.
  • They can cling to the rocks.
  • They can swim freely in the water.

The water is nutrient rich, and sunlight is abundant. Conditions here can support a variety of life forms.


     The animals will have shapes suited to their life strategies. Many simple animals are just tubes with openings at each end so that food can pass through and be digested. Such animals, though, are tender and fragile, a tasty morsel for a passing predator.

Some of them will learn to hide in the mud or will grow various kinds of protective shells. Shells may limit movement, however.

    Another plan of protection is a jointed exterior skeleton that encloses the body like armor. This is called an exoskeleton. Crabs and lobsters have exoskeletons. The skeletons provide protection and support for the animal's soft tissues. They give form to its body. However, if the animal is to grow, it has to be able to get out of its exoskeleton somehow. It may grow a soft new exoskeleton underneath the hard protective one. Then it sheds the old one, leaving a little time for the soft new skeleton to stretch out into a larger size before it hardens.


Fishes have interior skeletons, as do many land animals. Having bones on the inside gives the animal flexibility and provides anchors for the muscles. An endoskeleton can grow with the rest of the animal. However, interior skeletons (endoskeletons) do not provide exterior protection.

Water Animals  Information Menu

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© 1996,1997, 1998, 1999, 2000, 2002, 2003, 2004.   Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at .