Worms7th Grade Biology

Objectives & TermsIdentify the three main phyla of

worms.Describe the characteristics of each

worm phylum.ParasiteHostScavengerAnusFree-living organismClosed circulatory system

Characteristics of WormsBiologists classify worms into three

major phyla.FlatwormsRoundwormsSegmented WormsFlatworms belong to the phylum

Platyhelminthes.Roundworms belong to the phylum

Nematoda.Segmented worms belong to the phylum

Annelida.

Body StructureAll 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.

Nervous SystemWorms 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.

ReproductionBoth 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.

FlatwormsFlatworms 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.

ParasiteThe 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.

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.

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.

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.

TapewormsTapeworms 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.

RoundwormsNext 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.

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.

Segmented WormsEarthworms 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.

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.

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.