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

Designing Your Water Animal
Designing Your Water Animal

Animals are more complex than seaweeds, and they can evolve into many forms in the sea.

     Animals are more difficult to design than seaweeds, but they are more fun, too.  Be sure to think carefully as you work.  Everything has to come from something already in the ancestor, or be something that could logically evolve.  For example, a fish will never evolve into a crab, and a crab will never evolve into a fish, because their body plans are too different and evolution generally goes forward, not backward.  Once you have a basic body plan, develop the shapes and life styles that could logically come from it.  

It helps to talk your ideas over with your partners and to make some sketches before you do the computer work.  Save time and do the thinking first.

Part One: Design the Basic Ancestral Animal

Design Step 1: Create a Single Cell.


Begin with some primitive animal cells. Include the nucleus and some organelles.

I have named this cell species The Blob. It will be the ancestor of all my animals.

Design Step 2: Sketch a Clump of Cells.

Cut, paste, reduce -- now you have a clump of cells!


Design Step 3:  Play with the Idea of Shapes
Reduce the size of the cells and put more of them together.
Play with shapes a bit. 

Could this somehow be the beginning of an organized life form?

It is still very small.

Design Step 4:  Make a Simple Animal

Reduce the size of the cells further and combine them to make a blobby little animal.

We have a tiny animal here. It is about a quarter of an inch long, and semi-transparent. It has short, fine bristles. It also has brown light sensitive spots running down its body. It crawls and oozes along. This is a plant eater. Its mouth is on the end at the right. This is the ancestral animal. I have named it the Lumpy Crawler.

It lives among the rocks in a warm, shallow sea with not much wave action.

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 Design Step 5: Start Thinking About the Environment

Where does this little animal live? It is probably crawling around in the shallow water plants growing on the rocks. It eats the plants (that I made last week.) It has short bristles for protection. But does it have a future?

Design Step 6: What about Reproduction?

These little animals reproduce both sexually and asexually. They have a pair of special organs that make eggs or sperm. Eggs and sperm pass out of their bodies through pores in a fold on the sides of their bodies.

Sexual Reproduction: If food is plentiful they make eggs and sperm which they release into the water when they meet another animal of the same kind. Each parent contributes half of the chromosomes, so the new animals combine the characteristics of their parents and differ from each other.

Asexual Reproduction:  When food is scarce, these little animals may not find others of their kind. They release cells which have a full set of chromosomes identical with that of the parents. All of the young who survive will be clones of the parent and identical with each other.

 Part Two : Diversify into More Niches

    Biome One: The Jumping Muncher lives in Shallow Water

Adaptation Step One: Begin with Primitive Ancestral Animal.


We start with the Lumpy Crawler, the small animal that we have already developed.

It is about to become an ancestor!

Adaptation Step 2: Document Important Changes in Body Form

After millions of years, the little animal has a brownish mottled skin, making it hard to see. It has short spines for protection. It is a herbivore, and still lives in the shallow water among the rocks.

It has developed a stiff tab on each side of the front of its body and another at the back end of the animal. It uses the front tabs to drag itself along, and pushes with the back tab. Mobility has improved.

It can tell light from darkness because of eye spots on its sides.

Adaptation Step Three: Show Improvement in Fitness to Survive

Many millions more years have gone by.

The tail of the jumping muncher is now tucked under its body, and can be used to push the animal forward quickly.

The little herbivore is now about two inches long.

It can see movement in the environment, so it sees its predators.

Reproduction is now mostly sexual, as the animals are successful enough to be able to find mates most of the time.

    Niche Two: Tentacle Mouth Eats Everything!

Adaptation Step One: Begin with the Primitive Ancestral Animal.


This is the Lumpy Crawler that evolved earlier.

It is a tiny plant eater that lives in the rocks in shallow water.

Adaptation Step 2:   Show Differences in Structure

The animal is developing short tentacles for grasping food and pulling itself over the rocks. It is eating plants and bits of debris.

It continues to live among the rocks in shallow water but has expanded its range into the deeper off-shore waters.  Its color is changing to help it to be invisible among the brown seaweeds.

Adaptation Step Three: Show Development of Adaptive Structures
Tentacle Mouth Two

Millions of years have gone by.

The tentacles are working -- they are longer and stronger. The animal is bolder, sometimes catching and eating smaller animals. It is growing plates of shell on its back. It is still living among the rocks and seaweeds

. The eye spots in front of the body see movement.

Adaptation Step Four: Note How Evolution Continues
Tentacle Mouth 4

Millions of years have passed.

The animal is well adapted to its home among the rocks and seaweeds. It is protected by a shell over its body, and has long, flexible tentacles to help with locomotion and the capture of food. It eats plants and animals.

Reproduction is mixed, both asexual and sexual. There are many of these animals around in the warm shallow seas, but they move slowly, and so may have difficulty finding each other, especially among the taller seaweeds.

Niche Three: Razor-Strap: a Carnivore

Adaptation Step One: Begin with the Primitive Ancestral Animal.


Can the Lumpy Crawler evolve to change in yet another way?

Adaptation Step 2:   The Animal is Getting Longer.

carnivore one

Millions of years have passed. The animal is getting longer and thinner. It can move more rapidly through the rocks. It is beginning to eat other animals.

It reproduces sexually so that its many children differ from each other. The fastest and most ferocious become the parents of the next generation.

Adaptation Step Three : Adaptation Continues
carnivore 2 Over more millions of years the animal gets longer, thinner, and faster. Its spines begin to support a band of skin that helps stability when it swims. It is beginning to be a predator, chasing down other small, moving life forms. It can see its prey moving in the water. This is a new species of strap swimmers.  It is venturing out further from the shoreline and exploring new environments.

Part Three: Diagram Relationships

chart of animal family This chart shows the family tree of these animals and how they are related to each other.

They could continue to evolve and diversify out into many different species of descendents.

They could change in order to adapt to new environments.

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© 1996,1997, 1998, 1999, 2000, 2002, 2003.   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 .