1. Worms
7th Grade Biology

2. Objectives & Terms Identify the three main phyla of worms.
Describe the characteristics of each worm phylum.
Parasite
Host
Scavenger
Anus
Free-living organism
Closed circulatory system

3. Characteristics of Worms
Biologists classify worms into three major phyla.
Flatworms
Roundworms
Segmented Worms
Flatworms belong to the phylum Platyhelminthes.
Roundworms belong to the phylum Nematoda.
Segmented worms belong to the phylum Annelida.

4. Body Structure
All worms are invertebrates, with long narrow bodies without legs.
Worms have bilateral symmetry.
They have a tail and head end.
They have tissues, organs, and body systems.

5. Nervous System
Worms are the simplest organism with a brain, which is a knot of nerve tissue located in the head end.
Because the brain and some sense organs are in the head, worms can detect food, mates and predators quickly.

6. Reproduction
Both sexual and asexual reproduction are found in the worm phyla.
In many species there are separate male and female animals.
In other species, each individual has both male and female sex organs.
A worm with both sex organs usually does not fertilize its own eggs.
Instead two individuals mate and exchange sperm.
Some reproduce asexually by breaking into pieces.
Some worms can be cut into pieces and a whole new worm will grow from each piece.

9. Flatworms Flatworms are flat.
They include tapeworms, planarians, and flukes.
Tapeworms can grow to be 12 meters long, other flatworms are too small to see.
All flatworms are flat and soft as jelly.
Many flatworms are parasites.
A parasite is an organism that lives inside or on another organism.

11. Parasite
The parasite takes its food from its host, the organism in or on which it lives.
They rob their host of food and make them weak.
They may injure the host’s tissue and organs, but rarely kill their host.
All tape worms and flukes are parasites.

14. Flatworms Cont…
In contrast some flatworms are free-living. They do not live on or in other organisms.
Free-living flatworms may glide over rocks in ponds , or slide over damp soil.
Some swim in the ocean, and are brightly colored and are ruffled.

17. Planarians Planarians are free-living flatworms.
Planarians are scavengers-they feed on dead or decaying material.
They are also predators and will attack anything smaller than themselves.
It feeds like a vacuum cleaner.
It glides onto its food and inserts a feeding tube into it.
Digestive juices flow out of the planarian and into the food.
These juices break down the food while it is still outside the worm’s body.
Then the planarian sucks up the partially digested food.
The remainder of digestion occurs within a cavity in the animal.
Undigested food exits through the feeding tube.

18. Planarians Cont… On the head of a planarian you can see two dots.
These dots are eye spots.
The eye spots can detect light, but cannot see a detailed image.
The head also has cells that pick up odors.
Planarians rely mainly on smell.

19. Tapeworms Tapeworms are a type of parasitic flatworm.
A tapeworms body is adapted to absorbing food from the host’s digestive system.
Some can live in humans.
Some live in more than one host in their lifetime.

20. Roundworms
Next time you walk on a beach consider that 1 million roundworms live in each square meter of damp sand.
Roundworms can live in almost any moist environment.
Forest soils, Antarctic sands, and pools of super hot water.
Most are tiny and hard to see, but may be the most abundant animals on Earth.
Some are free-living and some are parasites.

22. Roundworms Cont… Unlike flatworms they have cylindrical bodies.
They look like strands of cooked spaghetti-pointed on each end.
Unlike cnidarians or flatworms, roundworms have a digestive system that is like a tube, open at both ends.
Food enters its mouth, and exits through an opening called the anus.
A one-way digestive system is efficient.
It acts similar to an assembly line.
A different part of the digestive process happens along the way out toward the end.
Juices break down the food, then it is absorbed into the animals body.
Finally wasted are eliminated.
This type of digestive system allows the worm to absorb large amounts of food.

23. Segmented Worms
Earthworms and other segmented worms have bodies made up of many linked sections called segments.
On the outside the segments look the same. On the inside some organs are repeated. Like the waste removal tubes.
Other organs like its reproductive organs are only found in certain segments.
All segmented worms have a long string of nerve tissue called a nerve cord.
They also have a digestive tube that runs the length of the worm’s body.
Like roundworms, segmented worms have a one way digestive system with two openings.

24. Segmented Worms Cont…
Segmented worms have a closed circulatory system.
In a closed circulatory system, blood moves only within a connected network of tubes called blood vessels.
Some animals such as snails and lobsters, have an open circulatory system in which blood leaves the blood vessels and sloshes around inside the body.
In both cases blood carries oxygen and food to cells.
In a closed system blood can move around the animals’ body much quicker.

25. Earthworms in the Environment
Earthworms tunnel for a living like many other segmented worms.
On rainy days they may come up out of their burrows.
They crawl on the ground looking for dead leaves and other decaying matter to drag under ground with them to eat.
Staying in moist soil helps keep their skin moist.
An earthworm obtains oxygen through moisture on its skin.
Earthworms are the most helpful animal to have in a garden.
They benefit people by improving the soil for plants to grow.
Earthworm tunnels loosen the soil, allowing air, water, and plant roots more room to move.
Earthworm droppings make the soil more fertile.