The Phylum NematodaMembers of this phylum are referred to as roundworms.

They have long, thin bodies that are

tapered at both ends.

Roundworms are pseudocoelomates.

They have a “false” coelom.

It is a hollow, fluid filled body cavity, but is only

partially lined with mesoderm

tissue.

Roundworms have a “tube within a tube” digestive system:

The digestive system has two

openings: a mouth and an

anus.

Food enters the mouth and

wastes leave the body through

the anus.

Examples of

Roundworms Include:

Ascaris Hookworms

Trichinella Pinworms

Ascaris

Where is this worm commonly

found?

Ascaris lives in the intestines of pigs,

horses, dogs, humans, etc.

What happens if Ascaris becomes too

numerous in the host?

They can completely block the intestine of the host.

A female can produce 200,000 eggs per day.

Hookworms

The hookworm’s mouth has cutting hooks that clamp to the intestinal wall of the host.

Hookworm’s feed on the blood of the host.

The larva live in the soil. They enter a host by boring through the bottom of the feet.

TrichinellaTrichinella species are the smallest

nematode parasite of humans, have an

unusual lifecycle, and are one of the most

widespread and clinically important

parasites in the world.

The small adult worms mature in the

intestines of a definitive host such as a pig.

Each adult female produces batches of

live larva, which bore through the intestinal

wall, enter the blood (to feed on it)

and lymphatic system, and are carried

to striated. Once in the muscle,

they encyst, or become enclosed in a

capsule.

Humans can be infected by eating infected

pork, horsemeat, or wild carnivores such

as fox, cat, or bear.

TrichinellaDon’t eat undercooked meat, especially PORK!

The best way to prevent trichinellosis is to cook meat to safe temperatures. A food thermometer should be used to measure the internal temperature of cooked meat. Do not sample meat until it is cooked.

Prevent Contamination

•Wash your hands with warm water and soap after handling raw meat.•Curing (salting), drying, smoking, or microwaving meat alone does not consistently kill infective worms; homemade jerky and sausage were the cause of many cases of trichinellosis reported to CDC in recent years.•Freeze pork less than 6 inches thick for 20 days at 5°F (-15°C) to kill any worms.•Freezing wild game meats, unlike freezing pork products, may not effectively kill all worms because some worm species that infect wild game animals are freeze-resistant.•Clean meat grinders thoroughly after each use.To help prevent Trichinella infection in animal populations, do not allow pigs or wild animals to eat uncooked meat, scraps, or carcasses of any animals, including rats, which may be infected withTrichinella.

Pinworms

Pinworms infect 16% of adults and 30% of the children living in the United States.

Since the eggs are laid on the outside of the body, the eggs may be stick to a person’s hands. Anything the person touches will become infected with these eggs.

Ways to control parasitic worms:

Good meat inspection.

Cook all meats thoroughly.

Wear shoes in areas occupied by host animals, such as barns, pastures, etc.

Wear protective clothing when wading in waters that may be infested with parasites.

Evidence of Parasitic Worms in

Humans

Compare and contrast the body plans of flatworms

with roundworms.

Similarities: Both have three germ layers and bilateral symmetry. They both have anterior and posterior ends allowing cephalization to occur.

Differences:

1.The roundworm has a body cavity called a coelom. It

is a false coelom (pseudocoelom) because it is not

completely lined with mesoderm tissue. A flatworm

has no body cavity and is called an “acoelomate”.

2.A roundworm has fluids that circulate through the

body; a flatworm does not.

3.A round worm has a tube within a tube digestive

system, with a mouth at one end and an anus at the

other end. A flatworm has a digestive system with only

one opening.

What is cephalization? What is the

advantage of cephalization?

Cephalization means that the brain and sense organs are concentrated in the anterior part of the body. This allows the organism to meet its environment head on, allowing quicker responses to the environment.

How can parasitic worms survive when they no longer have a digestive system? What is this concept called?

They have no need for a digestive system. They absorb food that has already been digested by the host. The loss of a body system is called “degeneration”.

How is the body shape of a

parasitic roundworm an adaptation

for its way of life?

The roundworm body is long and

slender and tapered at both ends.

This allows the roundworm to move

easily through the tissues of the

host.

How can a flatworm survive without a circulatory or a respiratory system?

A flatworm is so flat that none of its

cells are ever very far away from the

external environment. Oxygen and

carbon dioxide move by diffusion

between the body cells and the

environment.